Episode 7 Nature's Weirdest Events

We live in a very weird world.

And the more we discover about our planet,

the stranger it gets.

Every day, new stories reach us,

stories that surprise us...

What is that?!

'..shock us...'

PEOPLE EXCLAIM

..sometimes even scare us.

SCREAMING

Oh, my God!

We've scoured the globe to bring you the most curious creatures...

..the most extraordinary people...

I can stick almost anything to my skin without no glue.

..and the most bizarre behaviour...

..using eyewitness accounts and expert opinion

to explore a weird world...

..of unexplained underwater blobs...

..flying goats...

..and glow-in-the-dark fish.

We examine the evidence,

test the theories...

..to work out what on earth is going on.

In this episode,

we'll discover some real-life cave-dwelling dragons...

..unravel a shocking reindeer tragedy...

..and encounter mysterious blood-red rain in Spain.

-TRANSLATION:

-We were scared because we didn't know what was happening.

But first up,

a collection of the world's sweetest

and strangest love stories.

Meet Klepetan,

a male white stork.

Every year, he flies from Africa

to spend six months on this rooftop in east Croatia...

..a journey of over 13,000km.

Now of course, this in itself is not unique.

Millions of bird species all around the world

migrate with the warm weather,

but you see, it's not why

but who Klepetan makes this trip for

that makes this stork story so special.

This is Malena.

Klepetan's mate.

And every year, she waits patiently

on their rooftop for him to arrive.

It's a long-distance relationship

that's lasted for 14 years

and it's made them

THE most famous couple in Croatia.

-TRANSLATION:

-Nothing bothers them,

even the cameras,

which have been recording this phenomenon of animal love.

Their story has spread around the world.

Look at this.

The whole country is absolutely gripped

by this tale of avian adoration.

Who says romance is dead, eh?

But there's something strange going on here...

..because, well, our heroine

isn't the classic choice for a mate.

She's not able to do the one thing expected of a stork.

She can't fly.

The story starts back in 1993

when school caretaker Stjepan Vokic

found a female white stork on the side of the road.

She'd been shot by a hunter

and her wing was badly injured.

Stjepan named her Malena,

meaning "little one"

and although he nursed her back to health,

her wing never mended enough for her to fly.

And so Stjepan decided to take Malena under his wing, permanently.

Now, Stjepan didn't want Malena to miss out on motherhood

because of her disability,

so he built her a nest on his roof -

and it was here that she was spotted by Klepetan.

It was love at first sight.

STORKS CHITTER

And for 14 years,

Klepetan has arrived on March the 24th,

and he leaves six months later

to fly off with the other storks back to Africa.

-TRANSLATION:

-To cover all that distance,

and to come to the same place,

that's quite something for our brains to comprehend.

I'd get lost just trying to get to the nearby village.

But poor old Malena,

abandoned by her love?

Well, actually, she's not alone for long.

No. Whilst her mate's away,

Malena moves back in with Stjepan.

He catches her fresh fish,

and she stays nice and warm in his house,

watching stork documentaries.

She's taken into care every winter,

and stays at home whilst her partner migrates to Africa for the winter.

And then put back on the nest

every spring,

and then the male comes back and...

usually up to the hour of the arrival time of the previous year,

and there she is to welcome him.

-TRANSLATION:

-When he landed, it was pure joy.

I was relieved not to have to think about where he was.

I immediately took him some fresh fish.

So, why is Klepetan so devoted?

What keeps him coming back to this one particular female?

Well, it's all to do with Malena's alternative lifestyle.

The fact that she's been resting

and putting her feet up indoors all winter,

and being fed, probably means

she's in very, very good breeding condition compared to other birds

who have made a long and risky migration.

Whilst an average stork mother might hatch three or four chicks,

Malena raises a full nest -

at least five chicks every year.

Even though, to you and I, she looks a bit damaged

because she can't fly,

to him, she's in fine form for breeding.

And it's not just Malena that Klepetan's returning for.

Stjepan is also a bit of a catch.

He's built them their own shelter,

to protect the eggs that Malena can't protect with her broken wing.

He even travels over 30km to fish for food for the stork family.

In fact, Klepetan has stopped going out to hunt.

Instead, he prefers to have full board at Hotel Stjepan.

Yes, Klepetan might have to fly 13,000km to get here,

but life on this Croatian rooftop -

well, it's pretty sweet.

What a lovely story.

Thanks to one man's care and kindness,

this stork couple have produced chicks for the last 14 years.

Top work.

But whilst this love story played out in Croatia,

a love triangle was uncovered

in a South American forest.

2014, the Amazon.

There is an insane amount of diversity out there -

there's butterflies and beetles and spiders and ants -

and you can't take two steps without, like, finding something.

Aaron was conducting biological surveys

when he stumbled across something

he'd never seen before.

I just sort of casually walked past this tree,

and this tree had these yellow, bulby things popping out of the bark...

And I don't know if it's a fungus

or if it's a fruit produced by the tree.

One tree was covered in small, yellow balls -

each one the size of a pea.

I thought at first, "This is just some fungus,

"it's some weird fungus growing on the side of a tree,

"probably nothing more."

That was my first impression,

"It's just some sort of weird-looking mushroom."

To help him identify these strange spheres,

Aaron sent photos to a number of botanists.

Most were flummoxed,

but one recognised the weird, yellow structures.

I got this one e-mail back, and it was this botany professor,

and he said, "Oh, I saw this for the first time

"when I was a grad student working in South America.

"It is actually a rare, parasitic plant."

So, not a fungus at all,

but something much stranger.

Most of the world's plants get their energy

from a process called photosynthesis.

They produce sugars in the presence of sunlight,

but this thing's different.

It doesn't need to do that because it's a parasite.

It gets its energy

from the tree itself.

But then, every now and again,

it's got to burst out and reproduce.

It only bursts out through the bark of its host plant about once a year,

and that's when it flowers.

So these odd, yellow bulbs

are actually the flowers of this rare, parasitic plant.

But that was just the beginning

of some truly bizarre biology.

When Aaron went back to the tree at night...

he discovered small caterpillars

munching on the yellow buds...

..and they weren't alone.

Every caterpillar you find on this tree,

you'll find its own, like, designated ant.

Each caterpillar had an ant companion drumming on its back.

So what's going on here? Is this some sort of crazy ant orchestra?

Is this a caterpillar massage parlour?

Well, obviously not,

but watch very closely

because this is supremely interesting.

After playing percussion on the caterpillar's back,

a small drop of liquid emerges

and the ant drinks it up.

So, what's going on?

The caterpillars have special organs

that actually secrete, like, sugar water almost.

It has sugars, it has amino acids -

it's this really nice cocktail

that they produce just for the ants.

So, why are these caterpillars

providing the ants with this sweet syrup?

What's in it for the caterpillars?

Well, the ants, you see,

are the caterpillars' bodyguards.

They're paying for protection,

they're protecting them from parasites,

hungry wasps,

spiders, that kind of thing.

This is an example of a relationship

that we call myrmecophily.

Myrmecophily -

it means "ant lover".

And Aaron just happened to be in the right place at the right time

to stumble across this bizarre threesome.

What's unusual about this

is there are so many layers

to this biological scenario.

You have a tree,

you have a parasite that lives inside of the tree,

then you have a caterpillar that comes along to feed on these bulbs,

and you have ants that take care of the caterpillars.

Like, that's insane, right?

So, there's this entire ecosystem going on in just this one tree.

But there's one final, weird twist in this interconnected tale.

While I was just watching

this caterpillar-ant relationship going on,

something happened that just blew my mind.

There was a butterfly that landed on the tree.

I realised that it had this wing marking,

this yellow spot on its hind wing

that looked exactly like this parasitic plant.

Yes...

The adult butterfly of the caterpillars

that eat the parasitic, yellow bulbs

have their image emblazoned on their wings.

Now, it might just be a happy coincidence or camouflage,

but, come on,

it is totally weird.

Incredible.

Absolutely incredible.

What an amazing collection

of interconnected relationships.

You know, I always say that science

is the art of understanding truth and beauty,

and the truth about this beauty

is absolutely phenomenal.

And clearly South America is a hotspot

for stories of unusual ardour,

because here we're staying,

to listen out for a very peculiar serenade.

Deep in the cloud forest of Ecuador...

..at the foothills of the Andes,

a strange sound rings out through the mist...

TICKING

INTERMITTENT, MONOTONOUS BEEPING

And the animal responsible for this unusual call

is not what you might expect.

This is the club-winged manakin,

and there's something seriously strange about its song.

I saw the thing, I say,

"Really? Is that really happening

"or is it just my brain playing a trick on me?"

There is nothing like it in the whole natural world.

Joao had always been fascinated by the manakin's song

and, in 2011, he trekked deep into the forest to capture it on camera.

Every day, 4am in the morning,

we used to walk about 3km,

but it's like that,

so it took us a few hours to get there.

'I recognised the sound.'

I said, "OK, it's the bird."

He could hear the bird,

but filming it sing -

well, that was much more of a challenge.

It was very frustrating at the beginning,

because they move a lot,

they never stay, for more than a couple of seconds,

in the same place.

But then...

Bingo!

The bird just landed in a perfect place.

Now, watch this.

TICKING, MONOTONOUS BEEP

That sound...

isn't coming from its throat.

This bird sings

with its wings.

It's really hard to believe,

when you see the bird lifting its wings

and that thing happening,

it's...nothing like it,

there's nothing like it in the whole natural world.

So, just how does it produce a note from its feathers?

It's just a fantastic and fascinating sound.

They hit their wings together,

first, very briefly,

so they make a tick -

then they hit their wings together for a longer time period

to make this drawn-out...

toot.

TICKING, BEEP

Joao captured this movement in slow motion...

..and you can clearly see the wings

vibrate incredibly quickly.

This bird is doing something called stridulating.

On each wing,

the club-winged manakin has one special feather,

with a set of ridges along its central vein,

and next to it another feather

that acts like a pick.

As the bird shakes the wing,

these feathers rub against each other to make that sound.

The pick feather hits a whole series of knobs on the file

and rubs one way and then back again 100 times a second,

and it hits 14 bumps each way as it goes.

And so what this does, in combination,

is it makes a pure tone - a 1.4 kilohertz tone.

The club-winged manakin

is the only species of bird, that we know, that stridulates.

It's a very similar system

to that used by grasshoppers and crickets.

These insects rub their legs together

to create that familiar chirping sound -

and, just like these noisy neighbours,

the manakin's display

is all about impressing the ladies.

To send a message to the female that they are there

and they're a good mate.

But why would a bird sing with its wings...

rather than its voice box?

Well, because that's what the female manakins like.

It has to do with evolution.

The females, for some reason,

they choose to mate with males that produce that specific kind of sound.

So, basically males that have that ability,

they reproduce disproportionally more

and, through their genes, they spread that trait in the population.

I mean, imagine trying to vibrate your wings at 100 times a second.

It would be exhausting.

So, a female manakin can safely assume that, the better the song,

the fitter and stronger the male.

And Joao was certainly impressed.

To be honest, I'm not a female manakin,

but I was in love with that display.

It was, like, the best day of my life.

I couldn't believe that I saw and filmed that bird.

Top bloke, and top bird.

So, a mind-boggling love triangle...

..the strangest serenade...

and a long-distance avian relationship,

supported by Stjepan.

The course of true love,

well, it's unbelievably weird.

Next up -

a collection of super-strange powers,

a woman who could quite literally hear herself think

and an animal with a secret, life-saving skill.

But first,

we head to Slovenia...

..and a Postojna Cave park.

Now, since 1823,

tourists have flocked here

to explore the park's eerie caverns.

And for centuries, there have been tales of dragons

living amongst the stalactites and stalagmites.

And hiding out in the depths of the cave,

this creature was believed to have been

the dragons' spawn.

In complete darkness,

hidden between the rocks,

lives the world's largest cave-dwelling animal.

It's also the cave's top predator.

Meet the olm,

a type of amphibian called a salamander,

peculiar, pale animals

that live in the deepest, darkest depths of the caves.

There were thought to be less than 100 wild olms in these caverns.

They're so rare that few people have ever got a glimpse of one.

I'm very sorry to say I don't have an olm -

they're way too rare -

but what I have got here is a creature called an axolotl

and, just like olms,

they're salamanders -

and the two species share something else in common,

they spent all of their lives in water.

Of course, other species of salamander do leave the water

and, over hundreds of years,

they've given rise to all sorts of myths,

some of them surrounding fire.

It's said that they can resist the flames.

Perhaps it's that

that's given rise to those ideas of them being dragons.

No-one knew much about these funny, little amphibians

and so Saso and his team

moved some wild individuals

into an aquarium

to learn more about their fantastic physiology.

Olms don't have lungs.

Instead, they absorb oxygen from the water through those feathery gills.

They are completely blind.

They use sensors around their mouth

to pick up electrical impulses

and track down their prey.

The life of an olm is really a simple life.

Try to find food, eat, conserve energy.

Try to find a partner, mate.

Conserve energy.

And if they can't find food,

olms are able to digest some of their own body.

It can reach an age of around 100 years,

survive without eating anything for ten years.

And their unusual abilities don't stop there.

Like the axolotl here,

if the olm loses one of its legs,

it can regrow it again from scratch.

And this,

coupled with the fact that no-one had ever seen one hatch

or a young one,

gave rise to the idea that olms were in fact immortal.

Now, of course, Saso knew this couldn't be true

but, in over 300 years,

no-one had ever seen a baby olm.

That was until 2016

when Saso discovered this...

..in his aquarium.

I never thought I would see the egg of the olm.

This little egg was big news...

..a once-in-a-lifetime opportunity

for Saso and his fellow biologists.

It took the female 60 days to lay 52 eggs.

Saso carefully transferred his precious clutch into a special tank.

It was a moment where your hand was not allowed to shake.

And four months later...

..success.

These are the first baby olms

ever captured on camera...

..and the Slovenians are so proud of their new discovery

that they've taken these tiny dragons to their hearts.

Yes, they've gone olm crazy.

You know, I've always wanted to see an olm

since I was a kid and I had them in my childhood encyclopaedias.

Highly specialised animals, dead weird.

It's a weekend in Slovenia for me.

From tales of dragons,

next up is a far more familiar animal -

but one with a super-weird superpower.

Back in 2009,

Claire Guest was taking her dog for a walk.

Something she did every day.

I've had Daisy since she was a puppy and we're very, very close.

But on this day,

Daisy behaved very strangely.

One day, we went out for a walk together, I had other dogs with me,

and lifted the dogs out of the back of the car

and they went off to run around the field, but Daisy wouldn't go.

And she kept staring at me

and then nudging at me, and nudging into my chest.

Daisy was repeatedly sniffing and pawing at Claire's chest.

Could she be trying to tell her something?

The incident played on Claire's mind,

so she decided to go and see a doctor

and that was to be a life-changing decision.

I was diagnosed with a very, very deep-seated breast cancer -

which, if Daisy hadn't drawn my attention to it,

would have almost certainly been life-threatening

because it was so deep-seated

that I wouldn't have felt it for a long time.

Clever Daisy had sniffed out Claire's tumour,

saving her life -

which, in itself, is quite extraordinary.

But it gets even weirder

when you discover what Claire does for a living.

The almost unbelievable irony here

is that, just a few years earlier,

Claire had set up a charity,

Medical Detection Dogs,

to train dogs to sniff out cancer.

Claire has always been interested

in training dogs for tasks involving scent.

She was convinced that they could be used to sense human diseases.

And now, she'd become part of her own story.

When Daisy sniffed out Claire's tumour,

it came at a crucial time.

She was facing a lot of doubt

from the medical profession.

Following the early work that we'd done,

there was a lot of scepticism

and I could have given it up,

but Daisy saving my life changed things again for me.

It made me realise that, without the science of Daisy's nose,

I may well not be here today -

and it inspired me to keep going.

Of course, we all love our canine companions -

here are my two, what a couple of beauties -

but how do we get dogs to diagnose cancer?

Well, we already exploit the dog's amazing sense of smell,

sniffer dogs at airports...

..rescue dogs in disaster zones...

..but medical detection dogs

don't directly sniff out disease on human scent.

They're trained to smell urine samples.

We have a training area,

and the training area has a surgical steel carousel,

and this is where we put the samples onto.

So, here are the eight samples.

Only one of them indicates cancer.

This clever canine sniffs each sample in turn,

only stopping when she detects a positive result.

It takes an amazingly short amount of time to screen the sample.

In fact, if a sample is a negative sample,

it takes under half a second.

If it's a positive, it takes just under a second.

Good girl. Good girl.

Yay, good girl! Come on, then, Kiwi.

Good girl.

'Here, they are sniffing for prostate cancer

'and the data is exciting.

'These super sniffers are accurate over 90% of the time.'

So, why do dogs have the ability to sniff out cancers?

Perhaps, deep in their evolutionary past when they were hunting,

it allowed them to sniff out the weak and the ill amongst their prey.

Or perhaps, within the pack,

it allowed them to sense any weakness in the alpha members.

These days, of course, we are still a pack, we are the alpha members,

and it's that

that makes them unsettled.

Now, training a dog to smell urine samples is one thing

but, in Claire's case,

where the cancer was hidden deep in the body,

there's no physical sample to test.

So, what was it that Daisy detected?

Well, the team are still unsure

but they think that it's most likely she smelt it on Claire's breath.

And it is possible.

A dog's nose, after all,

is so much more sensitive than ours.

We can detect the equivalent of a teaspoon of sugar in a cup of tea.

But a dog, well,

it can sniff out the same amount

in two Olympic-sized swimming pools.

And Claire is convinced that this extraordinary sense

could be the answer

to a faster diagnosis.

If we can show that dogs can do that

over a large sample size

with a large number of patients,

this could be something we could offer,

a service that we could offer in the future.

Why not use the power of a dog's nose,

provided the dog's enjoying his work

and he's giving a reliable answer?

Dogs have the most remarkable biosensor,

their nose,

and sometimes you just can't improve on nature.

Next up, a much more unwelcome super sense.

March 2014.

Indiana, America.

Photographer Rachel Pyne

was relaxing, watching TV,

when she suddenly noticed something very strange.

I could hear my eyeballs moving every now and then.

I was just watching a TV show

and I wasn't even moving my eyes

but I heard them, like, screeching around

and I'm like, "Mom, like, I don't know what...

"I don't know what this is."

Yes, that's right.

Rachel could hear her eyeballs moving.

And she was also troubled by other weird body sounds.

My heartbeat

I could hear constantly.

It was like a "boom, boom, boom" all the time in my ears.

I could hear my food going down my throat.

I had some kind of ringing in my ears.

Just imagine.

Imagine hearing your eyeballs constantly moving in their sockets,

your neck muscles creaking every time you move your head,

your heart booming in your chest incessantly.

It would be horrific.

For Rachel, this wasn't just disconcerting,

it was debilitating.

As well as internal noises,

Rachel also became super-sensitive

to external sounds.

Some would make her so dizzy she would pass out.

Taking a shower, I'd fall almost every time

cos the water hitting the floor

just was really loud in my ears.

Just going out to a store, I couldn't push a shopping cart -

it was too loud, the wheels on it.

It was a very worrying time for Rachel and her family.

I actually ended up in the emergency room

and they did a bunch of tests and said everything was normal,

"Everything's OK, you can go back home,"

but, to me, I knew my body and I knew that something was different.

You know, something was wrong.

The dizziness and super-sensitive hearing

were taking over Rachel's life,

so she consulted other doctors.

Some doctors thought that it was some kind of inner ear...

Just like an infection, maybe.

And then it kind of went on to maybe it was migraines,

even though I had no headaches.

And a lot of doctors just said, "We don't know,

"you might have to live with it."

But Rachel couldn't just live with this mysterious affliction,

its effects were overwhelming.

I couldn't work as much as I used to

and I couldn't hang out with family as much as I used to.

I couldn't go out to eat, I couldn't go to the movies,

I couldn't really do a whole lot.

I couldn't even go to the mall.

'Rachel was finally diagnosed with a rare condition

'known as superior semi-circular canal dehiscence,

'or SSCD.'

SSCD is an extremely rare disease.

In about 100,000 people,

one person will have it.

A lot of patients get told it's just in their head.

The irony is that it truly is in their head,

there's a small, tiny hole in the inner ear,

between the inner ear and the brain...

and if you stuck your finger in your ear, you would be in this space.

That leads to the eardrum, the middle ear, and the inner ear -

and the inner ear structures are the cochlea

and your semi-circular canals.

And if you look at your superior semi-circular canal,

here,

you can see that there's a clear hole.

It wasn't until the year 2000

that medical equipment, in the form of CT scanners,

became sensitive enough

to find these tiny holes

between the inner ear and the brain.

And up until that point, sufferers simply weren't believed.

There was no name for this condition,

and there was certainly not a cure.

You'd go around telling people,

"I have this disease, and I can hear my eyeballs move."

A, if they don't believe you, they think you're crazy,

and, B, once they believe you, they can't see it.

You look perfectly normal,

and yet you're suffering immensely.

And do you know what? First of all,

she had this incredibly rare condition.

Secondly, the hole between her ears and her brain

was much narrower than most people who suffer from SSCD.

And thirdly,

she had the condition in both of her ears.

Rachel underwent pioneering brain surgery

to close up the holes in her inner ears.

Dr Yang operated on each ear separately,

so Rachel endured two surgeries.

I'm inside her skull, and I'll come down to this point,

and I know that her hole is right there.

'We do this small, dime-sized hole'

to get down to the tiny hole between the inner ear and the brain.

We fill it with a little bit of bone wax,

we take a small piece of muscle as we're going in,

and we take a small piece of bone that we fracture from the skull,

and we cover this hole.

-Hello.

-Hi.

-How are you doing?

-Good.

-Good to see you, how are you?

Hello. I'm good.

'After Rachel's operations,

'she immediately noticed a difference.'

'As soon as I woke up, I knew the dizziness was gone.

'The second surgery actually cleared up all of,

'like, the internal noises,

'so that one actually took a couple of weeks'

for me to start realising that those were gone

and it was starting to be quiet in my head.

Rachel is expected to make a full recovery.

Life is really good now.

I'm back to my usual things -

I work my full-time job,

I play with the nieces and nephews,

I can do things with my family,

go shopping, go out with my friends,

so it's, like, completely back to how it used to be.

It's incredible to think, isn't it,

that such a small defect -

one tiny, tiny little hole

in someone's inner ear -

could lead to such a massive amount of suffering?

Immortal dragons,

super sniffers and super hearing,

all wonderfully weird superpowers...

..but to finish,

a collection of horror stories.

Blood rain falling in Spain...

..and a shocking tragedy in Norway.

But first, a curious tale from Peru.

The heart of the ancient Inca Empire,

and home to a myriad of magical myths and mysterious legends.

My grandfather tells me the story of Paititi.

The Spaniards went into the Amazon,

looking for the lost City of Gold.

They come back with these stories of giant spiders that ate birds,

trees so tall they blotted out the sun,

and one of the details in this legend of Paititi

was a river that boiled.

Bird-eating spiders sound pretty exciting,

but it was the boiling river

that really captured young Andres's imagination.

You know, at its widest, it gets to be at least eight metres wide.

That caught my attention.

It's probably about 90 degrees C.

That caught my attention, too.

Now, Andres grew up to be a geologist

and, with this mythical river never far from his mind,

he began to ask around.

So, I started asking colleagues,

people who should have known

if there was a boiling river in the middle of the Amazon,

and everyone said, overwhelmingly,

"Very unlikely. No, man, sorry."

But Andres refused to give up on the legend,

so he went back to his family to ask for help.

So, we're at a family dinner, and my aunt asks me about my research,

and how it's going, and I tell her, "Hey, you know,

"this river that boiled would have been cool, but it doesn't exist,"

and she goes, "No, that's not true.

"I've been there."

So, in 2011,

Andres and his aunt set out on an expedition

to find the mythical river.

Legend had it that the secret of its location

is guarded by the Shaman,

a Peruvian mystic.

Andres would need to seek his permission.

Ultimately, it was my aunt who led me into the jungle

to go seek the blessing of the Shaman,

so that I could go study their sacred river.

Hours of trekking led them deep into the heart

of the Peruvian Amazon.

They crossed plenty of rivers,

but none that boiled.

Andres was about to give up on his boyhood dream...

..when he turned a bend in the river

to find something extraordinary.

That much steam, at those high air temperatures,

could only mean one thing.

And all along the river bank,

more, rather gruesome, evidence.

Bodies.

You're walking around and you'll see, you know,

frogs, mammals, amphibians, birds, reptiles, whatever,

that has fallen in and has not made it out.

Had these animals boiled alive?

Andres immediately took readings,

and the temperature hit over 90 degrees centigrade.

Yes, a boiling river.

Not a legend, after all...

..but an extraordinary discovery.

But where had this super-strange,

superheated river come from?

Well, we do know that there are other hot bodies of water

on our planet.

Tourists relax in bath-like

39-degree pools in Iceland.

Monkeys in Japan enjoy a 40-degree soak

during the freezing winter.

But what these two hot bodies of water both have in common

is their source.

You see, most hot springs

are the result of volcanoes.

Magma, spewing from the centre of the Earth, superheats nearby water,

creating hot pools and bubbling rivers...

..but the nearest volcanic activity

to the boiling river in Peru...

Well, it's more than 700km away.

So, where does the heat come from

to boil all of this water?

Well, it's easy to forget that -

deep beneath our feet, at the core of the Earth -

the temperature is 6,000 degrees centigrade.

That's about the same temperature

as it is on the surface of the sun.

Water deep within the Earth's core -

or in this case, a flask -

is so hot that it rises.

Like blood running through human arteries,

it pushes its way through fault lines and cracks...

..eventually emerging onto the surface of the Earth...

..giving Andres his boiling river.

And this Amazonian wonder

flows hot for over 6km.

It's up to 25 metres wide

and five metres deep.

It's simply huge,

the world's largest thermal river.

The local indigenous people

have always known of the existence of this sacred river.

They've called it the Shanay-timpishka

which, in their language, means

"Boiled by the heat of the sun."

Although, perhaps it should be better called

"Boiled by the heat of the Earth."

But why here?

Why has all of this superheated water surfaced in this spot?

Well, Andres has made it his mission to find the answer,

to finally discover the science behind the legend.

It's amazing, you know,

as you breathe in this hot vapour,

you feel it going into your body

and filling up your lungs.

It is one of the most immersive experiences

that I have ever been a part of.

With a mythical mystery still under investigation in Peru,

we head to Norway

and a startling discovery.

The Hardangervidda National Park,

the largest high mountain plateau in northern Europe -

3,500 square kilometres of wilderness...

..and home to over 10,000 wild reindeer.

But, in August 2016,

this remote moorland

became the scene of a shocking event.

More than 320 reindeer

have been killed on a mountain range in the south of the country.

A ranger found the dead animals on a hillside.

323 reindeer, a whole herd...

..including 70 calves, dead.

It was a horrifying scene.

The Norwegian nature inspectorate rushed to the park

and took tissue samples.

Earlier in the year, the first case of CWD,

chronic wasting disease,

a lethal illness that affects the brain,

had been found in Norwegian reindeer.

Could this new affliction be to blame?

Well, the thing is, CWD

doesn't affect calves

and, in this mass event,

both calves and adults were struck down.

CWD?

Definitely not.

So how about hunting?

GUNSHOT

It is legal to hunt in this part of Norway,

but scientists at the scene

couldn't find a single gunshot wound.

So, no wounds,

no sign of disease.

What on earth could have caused this sudden die-off?

Well, there is one possible culprit.

Something that's to blame for mass tragedies every year...

..from thousands of fish in China,

poisoned by a change in water quality,

to vultures, maliciously targeted in South Africa.

Poisoning, accidental or otherwise,

kills hundreds of thousands

of animals every year.

But in the bodies of the reindeer...

not a trace.

So, if it wasn't down to disease

or poisoning,

what could have caused this mysterious mass death?

When scientists examined the reindeer,

they discovered something extraordinary.

Each and every one

had suffered from a sudden cardiac arrest.

But what could stop 300 hearts simultaneously?

Well, there is one thing powerful enough...

THUNDER CRACKS

..to cause this type of destruction.

And days before the reindeer were found,

the skies above Hardangervidda had been electrified.

Lightning storms produce up to a billion volts,

easily enough to stop a heart.

Combining weather reports with the necropsy results,

scientists concluded

that this natural phenomena

had to be the cause of death.

But there's a problem.

You see, these supercharged strikes leave their mark.

But on the reindeer,

not a single scratch.

And we're not just talking about one animal here.

How could lightning strike

and kill quite so many animals at the same time?

Well, the lightning didn't hit the animals directly,

it hit the ground and radiated through the top layers of the Earth

as a deadly ground current.

Now, electricity likes to take the easiest path

so, if a human had come into contact with this current,

it would move up one leg and then back down the other,

passing through the groin

and most likely missing the heart.

But having four legs -

well, that's a different story.

that gives the electricity more routes into the body,

and, worse, the reindeer's hearts

are also much closer to their legs,

increasing the chance of the charge reaching the muscle

and causing a cardiac arrest.

The animals most likely huddled together for safety from the storm,

tragically making the deadly ground current

all the more effective,

reaching all 323 reindeer

in a matter of seconds.

Of course, no-one likes to see

hundreds of perfectly healthy animals

cut down in their prime,

but I can assure you of one thing,

the electric shock that came from that lightning

would have stopped their hearts beating in just a few moments,

none of them would have suffered,

and it does display the fact

that the awesome power of nature

can be devastatingly destructive.

Yes, Mother Nature can surprise us

with some pretty horrifying results,

as our final story shows.

Fuente Encalada,

a sleepy Spanish village.

Residents here live a traditional way of life...

..and this is the water fountain,

the heart of the community,

where everyone gathers for a gossip.

But, in November 2014,

local residents woke up

to something truly horrifying.

Overnight,

water in the fountain

had turned blood red.

-TRANSLATION:

-We were scared because we didn't know what was happening.

'At first, the villagers thought it might be secret sabotage.'

-TRANSLATION:

-We thought it was one lady in particular

using a chemical to deter the kids, to stop them bathing.

But one villager, Joaquin,

noticed it had appeared after rainfall.

-TRANSLATION:

-I use buckets on my roof

to catch the rainwater for watering the plants,

but I realised that the water was red.

Red rains have been documented for centuries.

The Romans thought they were such an ill omen,

they took a really drastic response.

In 191 BC,

the historian Livy

writes that, after such a shower had drenched the Roman Senate,

"the Fathers decreed that the consuls

"should sacrifice full-grown victims

"to whatever gods it seemed proper".

Well,

human sacrifice seems a bit extreme,

doesn't it, really?

And it's not very scientific either.

But what does make the rain fall red?

Well, we do know that dust from deserts

can be whipped up into the atmosphere

and carried thousands of miles.

If there's enough iron oxide in the dust particles,

it can fall as red rain,

leaving a rusty residue in its wake.

But in Spain,

there was no dusty residue.

The red water only appeared in puddles and pools.

So, what was it?

Joaquin had his own theories.

-TRANSLATION:

-At first, I thought it was from the paint on the building,

but then I thought it might be chemicals from the local farmers.

He collected some of the water

and sent it off to be tested.

I was completely astonished...

..because I never saw something like that.

When Javier looked at the samples under the microscope,

he noticed something very strange.

Some of them were moving.

They are actually alive.

Yes, these tiny cells

are a freshwater microalgae

called Haematococcus pluvialis

and, when conditions are good,

the algae is green.

But when it becomes stressed

by strong sunlight...

it turns red.

The sunlight and the UV rays

are dangerous for this type of algae,

so the algae produces pigment,

astaxanthin,

in order to protect itself

from the sunlight.

And here it is, Spain's blood rain,

and you can see why people were concerned.

Except that it's not blood at all, of course.

This red colour is produced by a pigment called astaxanthin,

and it's used by the algae

to protect them from UV light.

So, I know what you're thinking,

"Hmm, it's pretty much sunny in Spain all the time,

"so why haven't people seen this red algae before?"

Well, here's the weird thing,

this algae isn't normally found in Spain at all.

In fact, Javier thinks it originated in America,

some 6,000km away.

So, how had it travelled so far?

These algae are transported by the winds and dropped with the rain.

Evaporation from lakes

can allow the algae to get into the air,

and then transport through thousands of kilometres by the winds,

until it arrives here in Spain.

Javier analysed the weather

and the wind directions,

and he thinks the algae came all the way across the Atlantic.

So, the villagers' fountains hadn't been contaminated,

they'd been transformed by a stressed-out American algae.

But there's one final twist,

this aggravated alga

harbours a secret superpower.

You know when you cut an apple in half,

the flesh on the inside goes brown.

Well, that's because it's oxidised

when it comes into contact with the air.

But look what happens if you put the other half of the apple

into a solution of astaxanthin.

It doesn't oxidise,

for the very simple reason

that astaxanthin is a powerful antioxidant.

And we know the value of these antioxidants

because we take them, typically in the form of vitamin C,

to protect cells in our body,

and that's exactly what's happening here.

The algae is producing its own antioxidant,

in the form of astaxanthin,

to protect itself.

And astaxanthin is a particularly strong antioxidant.

It's more than 60 times stronger than vitamin C.

In fact, the algae that fell in Spain

is grown commercially

and stressed on an industrial scale

to harvest astaxanthin,

which is then used in food supplements and cosmetics.

So, far from being a bad omen,

the red rain in Spain

could actually...

..contain the ingredients for a much longer and healthier life.

Blood rain.

Mass deaths.

Boiling rivers.

Horrifying tales

with simple, scientific explanations.

So, there you go.

It seems there's almost no end

to the baffling and bewildering array of events

that our planet can throw at us.

There's a cornucopia of the confusing and the crazy,

a bounty of the bizarre

and a profusion of the puzzling.

You get my gist.

The natural world is just plain weird.

That's weird.

Next time, we discover holes punched out of the sky...

Oh, my jeez, look at that.

..see that all that glitters isn't gold...

..and find out why these chimps are cuddling up to rocks.