Chris - That’s a fantastic question. Have you guys seen this?

Helen - Hmm. Yeah.

Dave - Quite often see white speckles in front of my eyes just when it’s dark.

Chris - This is what’s called an entoptic phenomenon.  In other words, it’s a visual hallucination, effectively which is arising from within your eyeball.  There’s a number of possibilities here.  I think that we could be seeing one of two things.  One is that if you stimulate your eye: because the retina’s very sensitive to pressure if you just push on the side of your eye you’ll see an hallucinogenic light display.  You can do it yourself just by pressing the side of your eye.  Try that.  If you press on the side of your eye you can see some interesting colours.  I’m not saying poke your eye out.  Just apply gentle pressure to the side of your eye.  This is because the retina is sensitive to pressure and I think it causes discharges of different bits of the retina which I think causes those visual hallucinations you see.  They’re just photo-receptors firing off as though they’ve seen light they haven’t really seen.

When you sneeze you’ve got air jetting out of your nose, ricocheting around at 100 miles an hour.  I suspect that the vibration of the air coming out of your nose probably impacts on air that’s in your sinuses which are like cul de sacs.  You pressurise the air in your sinuses.  This causes a shockwave, probably, to reverberate through your skull.  I suspect some of that shockwave might go into your eyes and it could therefore cause the retina to jolt a little tiny bit.  The fact that not everyone gets that and everyone does sneeze a lot says that it’s unlikely. 

I was poking round and I found a very interesting comment on the internet about someone called Scheerer and Scheerer’s phenomenon.  This is amazing because it’s used as a way of measuring blood flow through the retina.  What you see when you look at a lovely blue sky and nothing else in the visual world.  You see these little white speckles coming in they follow a very stereotype path.  If you keep watching them you’ll see that they all tend to take the same pathway: a wiggly line running in from one part of your retina to another.  They’re not random, they’re coming in and flowing.  These are white blood cells and what’s happening is because they’re very infrequent compared with red blood cells they only crop up now and then as these white blobs.  When you look at the blue sky the red blood cells which your blood vessels are full of absorb the blue light quite well.  The white blood cells which are infrequent don’t.  They reflect it and you see a white sparkle on your retina.  That’s why you see these white blobs when there’s nothing else in the visual world to distract you.

I wonder if what’s going on with that question is that maybe the sneeze provoked him to look at the sky and he then saw what’s called Scheerer’s Phenomenon.  People can be trained to look at a computer screen and track the number of white blood cells they see come across.  This can be used as a measure of retinal blood flow if you don’t have another fancy way of doing it.  Isn’t that amazing?

Helen - That is crazy.

Dave - The other kind of speckle I’ve noticed occasionally is if it’s very dark everything seems to be covered with a very fine speckle – a bit like noise on a TV screen.

Chris - That’s called prisoner’s or captives' hallucinations.  This is where your retina is tuning itself to the ambient conditions.  You know how you go from a bright room to a dark room and your retina (over the course of about half an hour) changes its sensitivity.  You couldn’t see in the dark but now you can.  That’s your retina tuning up the sensitivity of photoreceptors, making them more sensitive.  You use rods rather than cones.  You increase the connections between cells to increase the signal.  It’s a bit like if you take your radio and the signal coming out is not very good you turn the volume up.  What your eyes are effectively doing is turning their volume up to become more sensitive to the light that’s coming in.  Because there’s almost no light coming in you start to even see the noise that’s being made in your retina, even though there’s no signal there.  People who go in caves will say if you turn all the lights out in a cave so it’s genuinely jet black you see this a lot.  Prisoners who are kept in solitary as a form of torture – nasty stories from that.

Dave - I think basically it’s random chance.  If you start off with matter evenly spread out over the universe and everything’s moving round a bit randomly.  Some bit are moving a little bit in one direction, other bits are moving a little bit in another direction.  Some large areas will have ever-so slight spin in one direction and other large areas will have slight spin in another direction.  Then if that collapses with gravitational collapse if you’ve ever tried to climb into the centre of a roundabout in a playground it spins faster and faster.  If you’ve ever watched an ice skater when an ice skater moves all of her mass into the centre then she spins faster and faster.  This minute amount of rotation started off by a huge scale increases and collapses under gravity.  There’ conservation of angular momentum so it speeds up and speeds up.  Some galaxies will be spinning in one direction, others in another direction.

Chris - We should see a roughly equal proportion of each.

Dave - Basically random.

Chris - There should be some systems a bit like our solar system where instead of the planets going one way round the sun they could all be going the other way around the Sun.  But you shouldn’t ever see cosmic billiards going on where one planet’s going one way and the other’s going the other.

Dave - Unless...

Chris - Unless something catastrophic has happened.

Dave - I think on the individual solar system there’s quite a lot of catastrophic stuff which has gone on.  You’re probably talking more about galaxies sort of averaging to make it work.

Helen - That’s a great question.  There’s two things to consider.  That is they aren’t susceptible to their own venom in their own fangs because they don’t kill themselves every time they make some venom.  That’s pretty cool but also quite easy to understand.  We also have poisonous chemicals inside our bodies that don’t kill us.  They’re kept in certain areas, for example, our pancreas contains a deadly cocktail of enzymes.  If your pancreas bursts and they all come out then that can really spell a big problem for you and you start digesting yourself from the inside.  Because it’s kept in certain organs that are lined with cells that aren’t susceptible to those enzymes then you’re okay.  Once it gets into your digestive tract then you’re okay.

This is also why if a snake happens to swallow some of its own venom it will be ok ay because the venom is made of protein.  The enzyme, which is a type of protein, will denature when it gets into the strong acids in your stomach and break down the structure of those enzymes and stop them from working, stop them from being so deadly.

The other question is what if a snake accidentally bit itself or if another snake bit it?  The answer seems to be yes, they are susceptible to their own venom.  If it’s injected into their system they can be susceptible to it but some scientists have also found anti-venom inside snakes.  They can develop their own anti-venoms to their own venom but we don’t quite yet know how that happens.  It could be that they have a low level of exposure.  Accidentally biting themselves occasionally, as you do?

You can imagine there’s some selective pressure for a snake to evolve, maybe not from itself, but perhaps from its mate or something.

Chris - A good corollary is spiders, isn’t it?  We know that spiders are vulnerable to their own toxins.  A female can bite the male and kill the male with their venom.  I suppose the same could be true for snakes because these venoms are proteins that have been injected into the body.

Dave - That is a great question.  How does a taser work?  Most tasers work by shooting out two little darts.  Behind those two little darts are pieces of wire.  The idea is you get hit by the two darts.  They stick to you so they make a nice electrical connection to you.  Then the taser itself applies a high voltage between those two darts so the current flows between the two of them.  That causes your muscles to contract.  It’s probably high-frequency which disables most of you and you lock-up.  You can’t move.  Whether it would affect somebody with whom you’re holding hands – you might be able to feel a bit of a shock but it’s probably only very small.  Most of the current would be running between the two needles which are stuck into you.  Skin-to-skin contact isn’t a very good conductor.  You probably wouldn’t get a big shock at all.

Dave - There are a couple of differences between the moon and the Earth.  One of them is that there’s no atmosphere so you could cycle far faster and wouldn’t get slowed down by air resistance.  The other big difference is gravity.  Gravity on the moon is about a sixth as strong on the moon as it is on the Earth.  As far as I can work out basically that means if you’re cycling on the moon at 20 miles an hour it’s the equivalent to cycling on the Earth six times faster but in slow motion.  So it would be the equivalent of cycling on the earth at 120 miles an hour but in slow motion.

Chris - I don’t get that, what do you mean?

Dave - If you were cycling on Earth at 120 miles an hour and hit a small bump you’re going to fly up into the air.  The same thing would happen on the moon but at 20 miles an hour if you hit any bumps you’d fly up into the air.

Chris - You’d do that thing like in ET where he bicycles in the air.  You’d just have your feet going round on the pedals?  But you’d go farther for quite a while?

Dave - For quite a while, the same sort of distance if you were doing 120 miles an hour.  Also if you’re doing 120 miles an hour and you’re trying to turn around a sharp corner you wouldn’t have as much grip so you’d slide and fall over.  The same thing would happen on the moon: there’s less gravity so there’s less friction so if you tried to go round a corner at 20 miles an hour you’re going to have to do it very gently otherwise you’d slip and fall over.

Helen - It’s a great question and something that stirs up seafood lovers a lot.  You’ve got your oyster there, you’re shucking it away, squeeze of lemon juice and they say you should see it twitching if you put lemon juice on it which goes to show they can sense chemicals and they can sense things going on.

Do they feel pain? Great question.

I think the answer has to be probably not, we don’t really know.  They have a nervous system, they can respond.  They have no brain as such; they have two ganglia or masses of nerves around their body but not a central brain like ours.  I don’t think anyone can possibly claim that oysters are conscious, that they have awareness like higher mammals (not just ourselves but other creatures like dolphins and things).  I certainly think there shouldn’t be a big problem with oysters.

There’s still debates going on about far more advanced creatures like fish.  Is it cruel to go fishing for fun?  Do they feel pain?  That’s the sort of thing where the debate goes on.  Scientists have found a lot of very sensitive receptors in the face of fish that we thing probably mean they can detect damage to their skin.  Whether that’s actually translated into pain is the big question we haven’t go to the bottom of yet.  Is it pain as we feel pain because they go ‘ouch.’ Or is it, ‘I know that’s going on: that’s something that’s not good and I need to do something about it,’ But not necessarily, ‘That really hurts.’

There was one study that does sound rather cruel but we do need to understand these things so they did it.  They took freshwater trout (this is scientists from the University of Edinburgh) and they actually injected bee venom into their lips to see what that did.  What they found was that these fish, compared to ones that just had water injected into their lips, they rubbed their lips on the bottom of the tank and on the gravel.  They didn’t go back to feed as quickly as the ones that just had water and they rocked.  In zoos sometimes or in older zoos when they weren’t designed to keep animals to keep them interested and stimulated they could develop a rocking motion to show that they’re not enjoying themselves.  A similar thing is happening with these fish.  Something is going on and I think they can sense pain.  It’s still a question we haven’t answered.

Chris - I think it’s in the answer you gave, Dave.  The way a taser works is to put two probes with very high electrical potential which means there’s a big potential difference between the two probes.  Most of the current in the taser is flowing from one probe to the other probe.  But the fence works slightly differently in that it’s putting a wire (or a cluster of wires) at a very high potential relative to the ground so that animals that brush against the fence feel a current flowing from the fence, through them to ground.  That’s uncomfortable and it puts them off. 

If you put yourself in the position of that animal you are holding onto someone and you touch the fence then both you and the person you’re holding onto have a connection to ground.  You’re offering a path to ground for the electricity flowing through the electric fence.  Therefore there will be a current.  Unlike the taser which has got the two probes, each of them with a higher amount of potential relative to one another.  It’s the ground that is the low potential and the fence that is the higher potential.  It’s a slightly different situation.

Chris -   The answer is, Theresa, that you can actually get signals coming from the visual system not just from the photoreceptors, the things that convert light waves into brainwaves; you can also get signals coming from all of the things that create the visual world for you.  That means the other bits of your retina (that are not harmed by whatever’s causing you to go blind), and you can also get them coming from the brain itself, in the same way as you can get tinnitus in your ears.  We think that might be a bit like phantom limb syndrome, for instance. 

There are a whole raft of reasons why people get hallucinations, and of course the normal hallucination that we all get, every time we go to bed at night, is that we dream!  This is where the bits of the brain that are involved in doing certain jobs during the day, when you go to sleep they become active again, and they re-play some of what you’ve been doing during the day.  That includes the visual parts of the brain that create the visual experience, so even though your eyes may no longer work, you may not be able to physically see, you still have visual memories, and those can still be played out and you can still experience them.  One of my friends who went blind at a young age said he loved going to sleep because it reminded him what colours were like.  He could experience colours again in his mind’s eye, so when people said something was read, blue or green he could understand and appreciate those colours again.

Helen - I don’t know

Dave - I guess it would be very hard to have someone in the brain scanner at the point when they have the ah-ha moment.

Chris - That’s true but actually it has been done.  It turns out it’s all down to the nerve transmitter chemical, dopamine.  What people do, in fact.  The first evidence for this people were asking people in the brain scanner to play a computer game where they had to shoot tanks.  Every time someone shot a tank they’d get some money and this is a rewarding result.  When people get that reward they get a little surge in dopamine which is the brain’s pleasure chemical.  There’s a part of the brain that’s tuned up to make you experience pleasure.  When something good happens this goes off like a machine gun and it releases this squirt of dopamine that makes you feel good.  When you have that ah-ha moment part of the pleasure of thinking, ‘I’ve cracked it,’ is all down to this chemical dopamine.  Amazing, isn’t it?

Dave - So you’ve got a reward for understanding things.

Chris - Exactly so that’s why we learn.

Chris - Thankfully, no.  Because otherwise Africa would have a much worse problem than it currently has where there are something like 4 million new cases of HIV every year.  They’re thankfully not caused by mosquitoes.  If they were we would all be in really serious trouble because it would be like malaria.  The reason is really simple because we know that mosquitoes are very good at transmitting viruses, certainly things like dengue gets spread by mosquitoes and that’s a virus.

There’s a very good reason why this isn’t the case with HIV which is that HIV is a very specialist virus which has on its surface viral velcro, molecular docking stations that lock on to certain parts of cells, CD4+ cells which you only find in us, in humans.  There’s related versions of HIV in chimpanzees (SIV) and they have their own specific cells that it locks onto.  Because those specialist cells are only found in us HIV is a very fragile virus.  It can’t survive in the mosquito’s intestine, it can’t latch onto cells in the mosquito, therefore the mosquito doesn’t get infected.  Therefore the mosquito can’t amplify the dose from the person it bites.  Therefore it can’t infect the next person because it can’t inject more viruses than it took in.  HIV is very poor at infectivity.  It’s actually very hard to catch, believe it or not.  You can reassure everyone you’re not going to catch HIV from a bite.

Dave - So this is how you separate oxygen from nitrogen in the air or helium.  The way that it’s done commercially is by cooling air down and all the different gases in air have different points at which they condense so carbon dioxide will come out first, then oxygen, nitrogen and argon.  If you slowly cool it down at different temperatures you take out different gases, different liquid gases.  Helium isn’t found in the atmosphere.  You can only find it in the top of oil wells.  It’s caused by radioactive decay.