0:00:05 > 0:00:08Humans are an incredible species.
0:00:08 > 0:00:10We've found ways to talk to each other
0:00:10 > 0:00:11on opposite sides of the world.
0:00:11 > 0:00:14We've discovered cures for terrible diseases,
0:00:14 > 0:00:18and some of us have even left this planet to explore space.
0:00:18 > 0:00:21But there's still so much left to find out.
0:00:21 > 0:00:24I'm Greg Foot. Ever since I was a kid, I've been into science.
0:00:24 > 0:00:27I've always been asking questions and taking things apart
0:00:27 > 0:00:29to understand how they work.
0:00:29 > 0:00:31I was the kid trawling through the rock pools
0:00:31 > 0:00:35and the one that tried to turn his bike into an aeroplane.
0:00:35 > 0:00:38I even went on to do a science degree.
0:00:38 > 0:00:40And I'm still asking questions.
0:00:40 > 0:00:42- This is going to hurt, right?- Yeah.
0:00:42 > 0:00:44And I reckon a lot of you are too.
0:00:44 > 0:00:46And that's what this series is all about,
0:00:46 > 0:00:48getting to the bottom of all those questions
0:00:48 > 0:00:52that never get properly answered, to reveal the secrets of everything.
0:01:00 > 0:01:03This time on The Secrets Of Everything...
0:01:03 > 0:01:04Can a loud noise kill you?
0:01:04 > 0:01:09I want to see the effect of sound on these massive pig lungs.
0:01:09 > 0:01:12The Doc and I launch our own space probe
0:01:12 > 0:01:14to find out why the sky is blue...
0:01:14 > 0:01:16Pick up the pace a bit, Doc, or we'll lose it.
0:01:16 > 0:01:18We're up to 33mph now.
0:01:18 > 0:01:21Come on, Harold. Come on, Harold.
0:01:21 > 0:01:23And I find out if it's ever OK
0:01:23 > 0:01:26to drink your own bodily fluids.
0:01:26 > 0:01:28Bottoms up!
0:01:29 > 0:01:31But first -
0:01:31 > 0:01:33the secrets of survival.
0:01:33 > 0:01:36You're walking down a dark alley, and you're set upon
0:01:36 > 0:01:38by a group of thugs. If you were in a film,
0:01:38 > 0:01:41you'd heroically finish them all off.
0:01:41 > 0:01:43But this is real life.
0:01:43 > 0:01:46Could you survive an unfair fight?
0:01:46 > 0:01:49The first guy, I'd distract him
0:01:49 > 0:01:53by showing him a picture of something incredibly ugly.
0:01:53 > 0:01:55I'd probably run around screaming a lot
0:01:55 > 0:01:57and just dodge them through speed.
0:01:57 > 0:02:00And then the other two guys that are standing next to the first guy,
0:02:00 > 0:02:02I'd slam their heads together.
0:02:02 > 0:02:05I would make sure I'm fighting with my hands and my legs.
0:02:05 > 0:02:06You can't just fight with hands.
0:02:06 > 0:02:10Try and beat them all up. And I reckon I'd do quite a good job.
0:02:17 > 0:02:20Now, in the absence of a bunch of Hollywood stuntmen,
0:02:20 > 0:02:23I've settled for a group of cage fighters from Liverpool.
0:02:24 > 0:02:30Leader of the gang is current mixed martial arts champion Rosi Sexton.
0:02:30 > 0:02:31She's hard as nails.
0:02:31 > 0:02:33That looked impressive.
0:02:33 > 0:02:35Just a bit of fun, really.
0:02:37 > 0:02:40Before Rosi has "a bit of fun" with me,
0:02:40 > 0:02:43I'd like to get some idea of just how unfair
0:02:43 > 0:02:45this fight is going to turn out.
0:02:45 > 0:02:47You're going to need these.
0:02:47 > 0:02:48Er, great. Cheers, thanks.
0:02:48 > 0:02:51So, go and get changed and we'll see you back here in a minute.
0:02:51 > 0:02:54Now, I've not done a lot of punching before,
0:02:54 > 0:02:56but how hard can it be?
0:03:01 > 0:03:02So what we got?
0:03:02 > 0:03:07Got over eight there, so we've got 80G.
0:03:07 > 0:03:1080G. All right. Happy with that.
0:03:10 > 0:03:13'G is a way to look at force.
0:03:13 > 0:03:17'100Gs is what you'd experience in a 60-mile-per-hour car crash,
0:03:17 > 0:03:19'so 80's not a bad punch.
0:03:19 > 0:03:20'Beat that, Rosi.'
0:03:24 > 0:03:27Good. That's a 12G there, Rosi, so 120.
0:03:27 > 0:03:30Wow! 120G.
0:03:30 > 0:03:32And I'm going to be on the receiving end of that.
0:03:32 > 0:03:35'This is looking less and less like fun to me,
0:03:35 > 0:03:38'but those Hollywood heroes never back out,
0:03:38 > 0:03:41'and as it happens, I've got a secret weapon.'
0:03:41 > 0:03:43We all do. Adrenaline.
0:03:43 > 0:03:46It's the same thing that makes your heart race in extreme situations.
0:03:51 > 0:03:52'The scene is set,
0:03:52 > 0:03:54'the camera's rolling,
0:03:54 > 0:03:56'cue the adrenaline.'
0:03:58 > 0:04:00I reckon the adrenaline's shooting up already.
0:04:00 > 0:04:02I don't think I need to go in.
0:04:05 > 0:04:09'Adrenaline increases your breathing and your heart rate.
0:04:15 > 0:04:20'But it also triggers a sudden release of stored sugar...
0:04:22 > 0:04:24'..your body's source of instant energy.
0:04:24 > 0:04:28'It's all part of the body's fight or flight response,
0:04:28 > 0:04:30'because in situations like this,
0:04:30 > 0:04:34'you're either going to need to fight your best fight ever
0:04:34 > 0:04:37'or run the fastest you possibly can.
0:04:37 > 0:04:41'To be honest, I've felt on better form.'
0:04:41 > 0:04:42Ahhhh!
0:04:42 > 0:04:44It's like being in a food processor.
0:04:46 > 0:04:48'I might feel utterly rubbish,
0:04:48 > 0:04:51'but in theory, the adrenaline surge means I should be meaner,
0:04:51 > 0:04:53'faster and stronger than normal.'
0:04:53 > 0:04:57Let's check out the power while this adrenaline's going through.
0:05:01 > 0:05:03Yes, so that's, what, 110?
0:05:03 > 0:05:05- 110G?- Yeah.
0:05:05 > 0:05:09So there you go. That test shows that I went up from 80G before
0:05:09 > 0:05:11to 110G after the fight,
0:05:11 > 0:05:14with all that adrenaline racing through my body,
0:05:14 > 0:05:17so my response to that fear was
0:05:17 > 0:05:21to release all that adrenaline, make you stronger.
0:05:24 > 0:05:26'It's starting to look like the movies
0:05:26 > 0:05:27'aren't quite as daft as they seem.
0:05:27 > 0:05:31'Adrenaline has turned me into a superman after all.
0:05:31 > 0:05:33'Taking on mere humans, even two at a time,
0:05:33 > 0:05:36'is beginning to look a whole lot easier.'
0:05:37 > 0:05:40In the films, the hero's always being attacked
0:05:40 > 0:05:42by opponents from all sides.
0:05:42 > 0:05:47So what happens if I punch both of these at the same time? You ready?
0:05:52 > 0:05:53It's weak.
0:05:54 > 0:05:562G. That's rubbish.
0:05:56 > 0:05:59If you're punching two directions at once,
0:05:59 > 0:06:01you've only got the strength of your arms,
0:06:01 > 0:06:04and, relatively speaking, that's not very much.
0:06:04 > 0:06:06You can't put any of your large core muscles
0:06:06 > 0:06:09or the strength of your legs and your hips into it.
0:06:09 > 0:06:12You're just like that. It's just...
0:06:12 > 0:06:13- it's rubbish.- Yep.
0:06:13 > 0:06:15You're right.
0:06:15 > 0:06:18'So unless you're in a movie, or you can persuade
0:06:18 > 0:06:19'your attackers to take it in turns,
0:06:19 > 0:06:22'you're going to get hit, and that really is rubbish.'
0:06:24 > 0:06:27Now, it's not the punch but the shock wave that's going to get you.
0:06:27 > 0:06:30If you imagine that this bucket is your skull,
0:06:30 > 0:06:32and the water inside is your brain,
0:06:32 > 0:06:34if I hit there,
0:06:34 > 0:06:35you get waves.
0:06:35 > 0:06:38The impact spreads out from the point that I hit it,
0:06:38 > 0:06:40and waves travel across.
0:06:40 > 0:06:42They're called compression waves.
0:06:42 > 0:06:44Now, the real problem comes when those waves
0:06:44 > 0:06:46bounce off your skull, and when they collide
0:06:46 > 0:06:50it causes a massive decrease in pressure.
0:06:50 > 0:06:52Now, that might only be for a couple of milliseconds,
0:06:52 > 0:06:55but it is enough to boil your blood
0:06:55 > 0:06:57and to cause the tiny blood vessels to rupture
0:06:57 > 0:07:00that carry oxygen to your brain.
0:07:03 > 0:07:04'From your brain's point of view
0:07:04 > 0:07:08'it doesn't really matter if it's damaged in a fair or unfair fight,
0:07:08 > 0:07:11'it's just that if there are more of them than you,
0:07:11 > 0:07:13'the chance of brain damage goes up.'
0:07:13 > 0:07:16So, the best way to win an unfair fight?
0:07:16 > 0:07:20Well, predictably, it's to avoid getting in it in the first place.
0:07:42 > 0:07:45I'm really into my music, whether that's listening in the car
0:07:45 > 0:07:49or at a club or ideally at a gig or a festival,
0:07:49 > 0:07:50where the music is so loud,
0:07:50 > 0:07:53it gets your ears ringing for a couple of days.
0:07:53 > 0:07:56But if sound can cause long-term damage to your hearing,
0:07:56 > 0:07:59can it hurt the rest of me as well?
0:07:59 > 0:08:01And can a sound actually kill you?
0:08:12 > 0:08:16Sound is essentially a type of energy made by vibrations.
0:08:16 > 0:08:20When an object vibrates, it makes the air molecules around it vibrate,
0:08:20 > 0:08:24and it's similar to what happens when a water drop hits a puddle.
0:08:24 > 0:08:27It makes the water molecules around it vibrate
0:08:27 > 0:08:30and the ones next to them also move, and the ones next to them,
0:08:30 > 0:08:32and that makes the wave.
0:08:32 > 0:08:35'And the bigger the wave, the louder the sound.
0:08:37 > 0:08:41'Which is something stereo junkie Matt Sprigg knows all about.'
0:08:41 > 0:08:44God, this is really going to have some welly, isn't it?
0:08:44 > 0:08:47- Can we have a look indoors? - This is where the magic happens.
0:08:47 > 0:08:49Some daddy speakers. Look at them!
0:08:49 > 0:08:50Eight massive sub-woofers.
0:08:50 > 0:08:53- Can we have this thing on full blast?- Full whack, definitely.
0:08:53 > 0:08:57'I want to what 24 speakers' worth of bass sound can do
0:08:57 > 0:09:01'in a confined space, and I've invited a friend along for the ride.
0:09:02 > 0:09:05- RATTLING - 'Matt is playing the frequency so low
0:09:05 > 0:09:07'that you can't hear it on TV speakers,
0:09:07 > 0:09:11'but it's the sound that's messing up our dummy's hair,
0:09:11 > 0:09:12'and the noise you can hear
0:09:12 > 0:09:16'is the car rattling as the sound waves rip through it.'
0:09:16 > 0:09:19Wow. That has got some kick to it!
0:09:19 > 0:09:23That is just massive speakers moving huge amounts of air,
0:09:23 > 0:09:26and it just shows that all sound is is the movement of air.
0:09:26 > 0:09:28'Without protection,
0:09:28 > 0:09:31'the wave of air will tear right through your eardrums,
0:09:31 > 0:09:34'damaging your hearing forever.'
0:09:34 > 0:09:37But your ears aren't the only organ vulnerable to sound,
0:09:37 > 0:09:39and to show you that,
0:09:39 > 0:09:43I need something even more powerful than Matt's 24 speaker beast.
0:09:47 > 0:09:49'These speakers, usually used at festivals,
0:09:49 > 0:09:53'are capable of knocking out more than 150 decibels.
0:09:53 > 0:09:56'That's the kind of levels you'd get from a jumbo jet taking off.'
0:09:59 > 0:10:04I want to see the effects of sound on these massive pig lungs.
0:10:04 > 0:10:09We're going to blast them with low frequency, high intensity sounds,
0:10:09 > 0:10:12so that proper drum and bass kick,
0:10:12 > 0:10:14hopefully 150 decibels,
0:10:14 > 0:10:17which is even louder than you'd get at a music festival.
0:10:17 > 0:10:19'Pigs are often used for research
0:10:19 > 0:10:23'as their basic physiology is so similar to our own,
0:10:23 > 0:10:25'and because this level of noise is so extreme,
0:10:25 > 0:10:29'we've even had to have the building checked for structural safety.'
0:10:29 > 0:10:31Right, let's do this.
0:10:31 > 0:10:36'We're going to blast 128 hertz of low frequency sound at these lungs.'
0:10:36 > 0:10:38OK, everyone.
0:10:38 > 0:10:41Three, two, one,
0:10:41 > 0:10:42go.
0:10:42 > 0:10:45SOUND WAVE PLAYS
0:10:55 > 0:10:59All objects have a natural frequency that causes them to vibrate.
0:10:59 > 0:11:02It's known as their resonant frequency.
0:11:02 > 0:11:04For lungs, it's right down there.
0:11:04 > 0:11:07It's the sort of frequencies you get in bass music,
0:11:07 > 0:11:09about 128 hertz, to be precise.
0:11:11 > 0:11:13'If your lung vibrates like this,
0:11:13 > 0:11:15'it could collapse like a popped balloon,
0:11:15 > 0:11:16'which might be fatal.
0:11:18 > 0:11:20'And it's not just the lungs.
0:11:20 > 0:11:25'Look what happens when the stomach gets the 128 hertz treatment.'
0:11:28 > 0:11:32As sound travels through the air, it compresses and decompresses it,
0:11:32 > 0:11:34and it does exactly the same thing
0:11:34 > 0:11:37when it travels through the air in your stomach. You can only imagine
0:11:37 > 0:11:39what that would do to your bowel movements.
0:11:41 > 0:11:44So, loud music can have some pretty gory side effects,
0:11:44 > 0:11:48from bleeding ears to collapsed lungs.
0:11:48 > 0:11:50It probably won't kill you instantly,
0:11:50 > 0:11:53but it could be the start of a slow and painful death.
0:11:53 > 0:11:56But at the right volume, it's all good,
0:11:56 > 0:12:00so hopefully at my next gig, I won't lose control of my bowels.
0:12:01 > 0:12:03'Protect your ears.'
0:12:25 > 0:12:28'If you look at space from a spaceship,
0:12:28 > 0:12:32'it's black. But if you look at space from down here on earth
0:12:32 > 0:12:37'it's blue when it's not cloudy, and we call it the sky.'
0:12:37 > 0:12:42But why is it blue here but black right out there?
0:12:42 > 0:12:45Well, to find out, we need to take a journey into space.
0:12:47 > 0:12:50'To help me build a spaceship,
0:12:50 > 0:12:54'who better than a man who's a chemist, a practical engineer,
0:12:54 > 0:12:56'meteorologist, and...
0:12:56 > 0:12:59'Polish musician?
0:13:01 > 0:13:03'He is Doctor Zbigniew Szydlo.
0:13:03 > 0:13:05'I just call him Doc.'
0:13:05 > 0:13:09# I see a bad moon rising... #
0:13:10 > 0:13:13'Doc and I are on the way to see Steve Randall.
0:13:16 > 0:13:18'His weather balloons travel to the edge of space,
0:13:18 > 0:13:21'so we're hitching a ride to find exactly why
0:13:21 > 0:13:24'the sky changes from blue to black.'
0:13:25 > 0:13:27We'll send up a couple of these cameras in the payload
0:13:27 > 0:13:31and then we're going to analyse the footage that comes back.
0:13:32 > 0:13:35'As well as filming the colour of the sky,
0:13:35 > 0:13:37'we'll be taking other readings too.
0:13:37 > 0:13:42'This is a thermometer and this bit measures atmospheric pressure,
0:13:42 > 0:13:46'or, in other words, how much air is left above our craft.'
0:13:48 > 0:13:50And this, this is the crucial bit. This is the GPS.
0:13:50 > 0:13:53If we didn't have this, we wouldn't be able to find it again.
0:13:53 > 0:13:56and that is going to be our payload.
0:13:58 > 0:13:59A beauty.
0:13:59 > 0:14:05# Spaceman, I always wanted you to go... #
0:14:05 > 0:14:08'I've always wanted to launch a spaceship,
0:14:08 > 0:14:12'but I never thought it would look like this.'
0:14:16 > 0:14:18Brilliant.
0:14:25 > 0:14:26Follow that balloon.
0:14:26 > 0:14:29'Although we've now lost visual with Spaceship One...'
0:14:29 > 0:14:32It's just got to 5,200 metres.
0:14:32 > 0:14:36'..here at mission control, Steve's in constant contact.'
0:14:37 > 0:14:40It's currently just over 10,000 metres.
0:14:40 > 0:14:42'At 10,000 metres,
0:14:42 > 0:14:45'Spaceship One is over a kilometre higher than Mount Everest,
0:14:45 > 0:14:48'and when it gets to 20,000 metres, higher than any airliner flies,
0:14:48 > 0:14:51'the blueness that what we see from the ground as sky
0:14:51 > 0:14:55'is now just a thin line on the earth's horizon.
0:14:55 > 0:14:58'Up here, there's almost no atmosphere at all.
0:14:58 > 0:15:03'The helium in the balloon expands as it tries to fill the void of space.
0:15:05 > 0:15:09'Now the race is on, to recover Spaceship One's re-entry module
0:15:09 > 0:15:10'and harvest its data.'
0:15:10 > 0:15:12Pick up the pace a bit, Doc, or we'll lose it.
0:15:12 > 0:15:15Up to 33mph now. How quick's that?!
0:15:15 > 0:15:17Go on, Harold!
0:15:18 > 0:15:21So we've got to go to its kind of last known position,
0:15:21 > 0:15:25roughly, and then try to track it locally?
0:15:25 > 0:15:28Oh, hang on a minute...
0:15:28 > 0:15:29Brilliant.
0:15:29 > 0:15:31Success.
0:15:31 > 0:15:34OK, let's get it open. We need to look at the footage.
0:15:36 > 0:15:39'Doc and Steve now analyse Spaceship One's data
0:15:39 > 0:15:41'at mission control's research centre,
0:15:41 > 0:15:45'to find out why the sky gets blacker the further you go into space.
0:15:45 > 0:15:50'Straightaway, our video shows how the colour blue drains away
0:15:50 > 0:15:53'the higher the balloon gets.
0:15:53 > 0:15:57'But what about the other measurements? What about temperature
0:15:57 > 0:15:59'and atmospheric pressure?'
0:16:01 > 0:16:04Now, if we have a look at the precise colour measurements
0:16:04 > 0:16:08from those pictures, what we find is
0:16:08 > 0:16:11that the colour changes a lot
0:16:11 > 0:16:13as you go higher and higher and higher,
0:16:13 > 0:16:16until you're a lot higher and it doesn't change as fast.
0:16:16 > 0:16:20Temperature also changes as you go higher,
0:16:20 > 0:16:23but it kind of changes at a similar sort of rate
0:16:23 > 0:16:27until you get to the top and it doesn't change that much.
0:16:27 > 0:16:30Now, the air pressure, the thickness of the air,
0:16:30 > 0:16:32also changes as you go up,
0:16:32 > 0:16:33and it does so...
0:16:36 > 0:16:39..in a very similar way to the colour.
0:16:39 > 0:16:41And that's what it's all about,
0:16:41 > 0:16:45As the air gets thinner, our blue sky fades to black.
0:16:45 > 0:16:47So the sky is blue
0:16:47 > 0:16:50because of the thickness of the atmosphere above us
0:16:50 > 0:16:53and the light bouncing off all the air molecules and dust particles.
0:16:53 > 0:16:56Take away the atmosphere and the sky would be black,
0:16:56 > 0:16:59just like it is in space.
0:17:24 > 0:17:26Here's Professor Logic.
0:17:26 > 0:17:28How do you do, Professor?
0:17:28 > 0:17:31Professor Logic is a busy man.
0:17:31 > 0:17:34So much to see, so much to learn,
0:17:34 > 0:17:36so much to measure.
0:17:41 > 0:17:44Professor Logic loves measuring.
0:17:44 > 0:17:47What are you going to measure today, Professor?
0:17:51 > 0:17:54You want to know how big infinity is, so you're going to measure it?
0:17:54 > 0:17:58Professor Logic has tried to count to infinity,
0:17:58 > 0:18:00but every time he thinks he might have got there,
0:18:00 > 0:18:04he finds he can make it bigger by one.
0:18:04 > 0:18:07So he's left the Earth to see if he can see
0:18:07 > 0:18:10if space is infinitely big.
0:18:10 > 0:18:11There's a problem?
0:18:11 > 0:18:13If space really was infinite,
0:18:13 > 0:18:17it would contain an infinite number of Professor Logics,
0:18:17 > 0:18:19and you've never seen any.
0:18:23 > 0:18:26Professor, are these your animals?
0:18:26 > 0:18:28You're using them to see if it's true
0:18:28 > 0:18:30that an infinite number of monkeys
0:18:30 > 0:18:33actually could write the complete works of Shakespeare.
0:18:36 > 0:18:38Oh, dear.
0:18:38 > 0:18:40So near and yet so far.
0:18:42 > 0:18:47Professor, does it really matter that you can't measure infinity?
0:18:47 > 0:18:51I mean, it seems to me that infinity is a rather beautiful thing.
0:18:51 > 0:18:55A symbol perhaps of eternity, or maybe eternal love.
0:18:57 > 0:19:01Perhaps like a carousel that's turning,
0:19:01 > 0:19:04running rings around the moon.
0:19:04 > 0:19:06Like a clock whose hands are sweeping
0:19:06 > 0:19:10past the minutes on its face,
0:19:10 > 0:19:15and the world is like an apple whirling silently in space,
0:19:15 > 0:19:20like the circles that you find in the windmills of your mind.
0:19:24 > 0:19:25The trouble is, Professor,
0:19:25 > 0:19:28infinity isn't a number at all,
0:19:28 > 0:19:32more an idea that you can't measure.
0:19:32 > 0:19:35It certainly makes you think, doesn't it? Goodbye.
0:19:37 > 0:19:38ALARM BLARES
0:19:48 > 0:19:50BURGER BURPS
0:20:09 > 0:20:12Ah! You've been feeling really rubbish for days.
0:20:12 > 0:20:14You've got a stinking cold,
0:20:14 > 0:20:17Every time you sneeze, your whole body shakes
0:20:17 > 0:20:19and you just can't keep your eyes open.
0:20:19 > 0:20:23Does that mean the urban legend you heard as a kid is true?
0:20:23 > 0:20:27If you sneeze with your eyes open, will your eyes really pop out?
0:20:38 > 0:20:42'To find out I've asked my friend and serial sneezer Ella to help.'
0:20:42 > 0:20:44- All right, you up for this?- Yes.
0:20:44 > 0:20:47'First up, though, we've got to make ourselves sneeze.'
0:20:47 > 0:20:49I've read some stuff about this.
0:20:49 > 0:20:53- What is it?- This is ground white pepper.- Yeah, I'm ready for it.
0:20:53 > 0:20:56'Pepper contains something called piperine,
0:20:56 > 0:20:59'a chemical which really irritates your nostrils.'
0:20:59 > 0:21:01SHE COUGHS
0:21:01 > 0:21:02Oh...
0:21:04 > 0:21:06- Yes?- No.- No?
0:21:06 > 0:21:08Aaargh!
0:21:08 > 0:21:11I'm crying, but I'm not sneezing.
0:21:11 > 0:21:14'Clearly my sneeze threshold is quite high.
0:21:14 > 0:21:17'Time to try something different.'
0:21:17 > 0:21:19- This time, take the tissue...- Yep.
0:21:19 > 0:21:23..and twist it and shove it up and tickle the top of your nose.
0:21:23 > 0:21:25OK.
0:21:25 > 0:21:26OK.
0:21:28 > 0:21:30- I've got one coming.- Me too.
0:21:32 > 0:21:33HE SNEEZES
0:21:33 > 0:21:36- Were my eyes open or shut? - Definitely shut.- Definitely shut?
0:21:36 > 0:21:41'Just before you sneeze, you breathe in and your chest inflates.
0:21:41 > 0:21:47'When you finally let rip, it all comes rushing out at over 100mph.
0:21:47 > 0:21:50'That explains why your mouth moves so much in a sneeze,
0:21:50 > 0:21:53'but it's still not clear why your eyes shut.'
0:21:53 > 0:21:56Right. There's only one way we're going to do this.
0:21:56 > 0:21:58You're going to have to hold them open,
0:21:58 > 0:22:01I'll have to tickle. I'll have to see what happens.
0:22:01 > 0:22:03I really hope they don't pop out.
0:22:03 > 0:22:04I need them.
0:22:06 > 0:22:08HE SNEEZES
0:22:08 > 0:22:09Come on!
0:22:09 > 0:22:10That was open.
0:22:12 > 0:22:15'My eye only stayed open because it was forced to,
0:22:15 > 0:22:18'but there's a good reason why it didn't pop out.'
0:22:18 > 0:22:22Lucky for me, you've got muscles in your eyes that allow you to look up,
0:22:22 > 0:22:25down, those ones there, left, right,
0:22:25 > 0:22:29and also ones that keep it in place, so when I sneezed,
0:22:29 > 0:22:32- my eyes weren't going to go anywhere.- That's good.
0:22:32 > 0:22:34'Urban legend - rubbish.
0:22:54 > 0:22:58'There's nothing like a cool refreshing drink on a warm day.'
0:22:58 > 0:23:01But if I was stranded, alone,
0:23:01 > 0:23:03far from the comforts of civilisation,
0:23:03 > 0:23:06how long could I exist without drinking?
0:23:06 > 0:23:09'Imagine you're marooned on a desert island.
0:23:09 > 0:23:12'The only water you've got is what you can personally provide.
0:23:12 > 0:23:18'Would you, could you survive on your own bodily fluids?'
0:23:18 > 0:23:21I think it would be pretty disgusting, to be honest with you,
0:23:21 > 0:23:23but, erm, can't knock it until you try it, I suppose.
0:23:23 > 0:23:27- Might as well.- Pretty much. - I probably would, yeah.
0:23:27 > 0:23:29Yeah, I'd do it, because in my head I'd be like,
0:23:29 > 0:23:30"If I'm thirsty..."
0:23:30 > 0:23:32HE LAUGHS
0:23:32 > 0:23:35- I'd rather die.- No, I would actually do it.- No. I'd rather die.
0:23:35 > 0:23:38No, I'd rather die, thank you.
0:23:44 > 0:23:47'The BBC refused to pay for a desert island,
0:23:47 > 0:23:50'so I've come to the next best thing,
0:23:50 > 0:23:51'a lab in Wales...'
0:23:51 > 0:23:53- Hiya, how are you doing? - Hello.- I'm Greg.
0:23:53 > 0:23:56'..where Sam Oliver will make me thirsty enough to...
0:23:56 > 0:23:58'well, we'll see.'
0:24:00 > 0:24:03First thing we need to do is establish how much you weigh.
0:24:03 > 0:24:06'Sam's got a plan to extract as much fluid from me as possible,
0:24:06 > 0:24:10'and regular weigh-ins will tell him
0:24:10 > 0:24:11'exactly how much he's getting.'
0:24:11 > 0:24:1379.8 kilograms.
0:24:13 > 0:24:16'Now, I've not been to the loo for 12 hours.'
0:24:16 > 0:24:18I'm sure I can squeeze one out for you.
0:24:18 > 0:24:20'Time to open the floodgates.'
0:24:25 > 0:24:28It's nice and warm.
0:24:30 > 0:24:33I'm proud of that, Sam, that's a lot.
0:24:33 > 0:24:35That's exactly 800ml.
0:24:36 > 0:24:39'According to Sam, it's possible to pee out
0:24:39 > 0:24:41'up to two litres of urine every day,
0:24:41 > 0:24:45'so this lot would be worth its weight in gold on a desert island.
0:24:50 > 0:24:52'The trouble is, peeing isn't
0:24:52 > 0:24:54'the only way we lose fluid
0:24:54 > 0:24:58'so Sam's recreated my island paradise in a sealed chamber
0:24:58 > 0:24:59'heated to 30 degrees.'
0:25:01 > 0:25:04I'd like to be able to monitor your core temperature, and the...
0:25:04 > 0:25:06Thermometer, yeah?
0:25:06 > 0:25:09No...it's best to measure it rectally, actually.
0:25:09 > 0:25:11This is the probe I'd like you to insert.
0:25:15 > 0:25:17I feel violated.
0:25:21 > 0:25:23'The plan is to dehydrate me even more.'
0:25:23 > 0:25:25Keep going, that's really good.
0:25:25 > 0:25:28'We sweat from glands all over the body,
0:25:28 > 0:25:31'and the humidity in this Welsh desert island
0:25:31 > 0:25:33'is sending them into overdrive.
0:25:38 > 0:25:42'Worse still, as my breathing gets faster, I'm going to lose
0:25:42 > 0:25:45'even more moisture from my lungs.'
0:25:45 > 0:25:482...1...and stop.
0:25:54 > 0:25:58It's about 77.7.
0:25:58 > 0:26:00OK, Sam, so how much sweat did I lose?
0:26:00 > 0:26:03You actually lost just over a litre in sweat.
0:26:03 > 0:26:08So today, with urine, sweat and breath, I've lost
0:26:08 > 0:26:12just over two litres, am I now classified as dehydrated?
0:26:12 > 0:26:15Yeah. You're going to be around two and a half per cent dehydrated.
0:26:15 > 0:26:17'If I was on my desert island, I'd be in trouble,
0:26:17 > 0:26:20'and if I didn't drink anything for another four days,
0:26:20 > 0:26:22'I'd be dead.
0:26:22 > 0:26:25'So seeing as my pee is the only bodily fluid
0:26:25 > 0:26:27'I'd stand any chance of collecting,
0:26:27 > 0:26:30'it's time for a swig of the amber nectar.'
0:26:30 > 0:26:33So, erm, could I survive off it?
0:26:33 > 0:26:37I guess if it was your only fluid. It is sterile.
0:26:37 > 0:26:39It would be your choice, really, I think, Greg.
0:26:39 > 0:26:42Well, you know what, Sam? I've come this far.
0:26:42 > 0:26:44I may as well see this journey to the end.
0:26:51 > 0:26:52Bottoms up.
0:26:59 > 0:27:01Ahhh. Eurghh.
0:27:01 > 0:27:03How was that, Greg?
0:27:03 > 0:27:04GREG LAUGHS
0:27:04 > 0:27:09If my life depended on it, I could probably just about do that.
0:27:09 > 0:27:12'And then, at the eleventh hour,
0:27:12 > 0:27:13'Sam drops a bombshell.'
0:27:13 > 0:27:16Unfortunately, on a desert island, though, Greg,
0:27:16 > 0:27:18your urine's likely to be a lot more concentrated,
0:27:18 > 0:27:22and therefore might even make you vomit or cause diarrhoea.
0:27:22 > 0:27:27So, erm, you probably wouldn't drink your urine on a desert island.
0:27:27 > 0:27:32Thanks! You've just told me that after I drunk it.
0:27:32 > 0:27:34Cheers(!)
0:27:39 > 0:27:413, 2, 1...
0:27:41 > 0:27:43'There are still loads of secrets out there.
0:27:43 > 0:27:47'Next time - can body armour really save your life?'
0:27:47 > 0:27:49Did it stop the bullet?
0:27:49 > 0:27:52'Why boomerangs come back...
0:27:52 > 0:27:53'usually...'
0:27:53 > 0:27:54It may not look like it,
0:27:54 > 0:27:58but there's a lot of physics going on in this bent bit of wood.
0:27:58 > 0:28:00'..and surviving being buried alive -
0:28:00 > 0:28:02'all you need to know.'
0:28:02 > 0:28:04I just feel weak.
0:28:23 > 0:28:26Subtitles by Red Bee Media Ltd