Chris: -   The reason that you get wrinkly fingers in the bath is because the skin on your fingers and hands and toes is quite thick, and it’s there to protect you.   You have a slight thickening of the skin because we tend to rub our fingers against things more often than we rub other bits of our body with things and the skin becomes thicker there to compensate.   The top layers of that thickened skin are flat, dried-out, dead cells.  In fact, they're falling off of you all the time.  If you could total up the number of cells that you're losing, it’s about 40,000 skin cells a minute that fall off of you.  If you added them all up, that's 1 ½ stone in dead skin over a lifetime.

Now that dead skin on your fingers which is still attached, despite being a flattened thick layer, is nonetheless slightly penetrable by water, and water can get into that layer, and it makes the thin flattened cells swell up a bit.  And in the same way that if you make railway lines very, very warm, they can buckle and bend which is why you have to leave a gap between them, the skin cells to the same thing.  They swell up, they press into each other, and as a result, they push each other out of the way, and they get thrown up into all these ridges and folds because the cells are bigger, because they've got water in them.  After you get out of the bath or the sea, or the swimming pool, and you dry out again, that extra moisture that’s got into the cells comes back out, the cells flatten out again, and they go back to their normal shape, and that's why you go wrinkly in the bath.

Dave: -  I think the simple answer is it is possible they would protect you from an electric shock, but it’s not something I would ever recommend because it’s only “possible”.  If you have a big, thick rubber sole then you're quite insulated from the ground, and if there’s no path for electricity to flow through, you won't get a big current going through you, so you'll be fine.  It’s essentially a similar reason to why birds can sit on an electricity cable.  They might be sitting on a very high voltage, but there’s no path for electricity to get down to earth through them so they’re absolutely fine, there’s no current flowing.

So, as long as you're just standing on your shoes you're not touching anything else, your feet aren’t wet so they're not creating a short path around the rubber soles to the ground, and you're not accidentally touching anything metallic - If you were touching the outside of a toaster which might be earthed then you might get a horrible current going through the knife, up your arm, then down the other arm, then you might be okay.  But there’s so many things that could possibly go wrong, so unplug the toaster first.

Ben: -   I think that sounds like a sound advice, and that by and large, don't stick metal things in electrical appliances.

Dave: - It’s basically just a very long piece of fairly high resistance wire. I've taken a toaster apart recently so I know this. It starts at one end and kind of zigzags up one side, then the current flows down and then zigzags up along the other side, and then it’s attached to the neutral wire.  So, one end of it is going to be at 240 volts.  The other end is going to be at about earth.  So, if you stick something metal anywhere near the 240 volts, even 100 volts, you're going to get a big shock.

Chris: - But if you were lucky and you got it to the neutral end, the potential there is a bit lower.  So if you were making a toaster, hopefully, you'd design it with the most inaccessible bit of the high resistance filament, furthest away from where the knife’s going to go.

Dave: -  Looking at how the toaster worked, one of the holes is going to be more dangerous than the other one, but they didn’t seem to have made any particular attempt to make one side more difficult to get at than the other.

Chris: -  They assume people have got some common sense after all.

Ben: -  Exactly.  I guess if the general rule and the general understanding is, “Don't stick metal cutlery in your toaster” then the other safety features are probably obsolete!

Chris: -  Well we have looked at this as a news item on the Naked Scientists a couple of years ago.  There was a paper we reported.  I actually gave it the exciting title of “Fulsome flavours on offer at the “breastaurant”.  It was a piece of work done by a lady called Helene Hausner who is from the University of Copenhagen.  It was a paper published in the Journal of Physiology and Behaviour in 2008.  What she did was to investigate this very phenomenon because women, including my wife, who have had babies, often report that the certain things they eat will affect whether or not the baby is very enthusiastic to breastfeed or not.

To get to the bottom of this sort of transmission between food and breast milk flavourants, this group recruited 18 women who were breastfeeding at the time and they got them to give some milk samples before and then milk samples after they gave them some capsules containing various flavourants.  The flavourants they tested were menthol – we all know what that is - and also a chemical called d-carvone.  Carvone is the stuff that makes caraway seeds have that very aromatic flavour to them.  They also tested a chemical called 3-methyl acetate which is a banana flavour, and trans-anethole which is a sort of a liquorice taste.  It’s the thing that makes star anise and Ouzo have the liquorice taste the way it does. 

By feeding the women these things and then taking breast milk samples from them for certain amounts of time after, up to 8 to 10 hours, and then measuring the volatiles (the smells) above the breast milk, they could work out roughly how much of these flavourants were getting into the breast milk. It wasn’t trivial.  In fact, they found that different times elapsed for different flavours.  The menthol took about 4 to 6 hours to peak, d-carvone and the trans-anethole took about 2 hours to reach peak levels, but the banana flavour, the 3-methyl acetate, didn’t come through at all.

The interesting thing was that there was an 80% difference in the levels of these different smells and taste between different groups of the women.  So if you look at one woman and compare another woman for the same flavour, you might detect 80% more or less of that flavour in her breast milk compared with the other woman.  And if you do the test more than once on the same woman, you might find more than 50% variation in the levels of these different flavourants in their breast milk.  What this shows you, therefore, is that it makes a very big difference from one person to the next and it makes a very big difference even in the same person. 

But the bottom line is that things that you eat definitely can end up going into your breast milk, and it’s not just small molecules and flavourants; it’s also whole proteins.  Researchers back in the ‘70s did studies by radioactively labelling proteins and amino acids, sending them through in the diet, and tracing them out into breast milk, showing that they do then end up going out and going into the baby.  So, people who say their babies do develop tastes for things based on what mum’s been eating are absolutely right.

Ben: -   How well developed is a baby’s sense of taste?  Do you think that babies can actually taste this?

Chris: -   It’s almost certain that they can.  If you think about it, the baby, when it comes out, is very under-developed and tends to prioritise the development of the systems that enable it to succeed when it’s little.  So it tends to develop first the things that will be most essential to survival.  That includes knowing when something is good for you and bad for you, and how to alert mum with a cry.  And babies, if you want to encourage them to eat something, they've got to like what they're eating.  It’s a sort of reinforcing thing, isn’t it?  The brain has to say, “I like this.  I want to do it more” which makes sure the baby feeds regularly.  So it’s almost certain that babies do get hooked on these flavours.

Ben: - Some compelling arguments there, thank you very much, Beverly.  It’s a certainly one for you Dave, you're our physics guru.  You know a lot more about nuclear power than I do.  What are the arguments in its favour?

Dave: - It basically depends how bad you think burning coal is.  Burning coal actually releases more radiation into the environment than nuclear power ever has, even including things such as Chernobyl, because there’s a load of radioactive elements in coal.  You burn it, they get released.  There’s no way of constraining it.  Also, burning coal produces lots of carbon dioxide which is bad for all sorts of other reasons including the greenhouse effect, etc.  There’s also issues with acid rain which have been largely improved, but we’re getting huge amounts of our energy at the moment from fossil fuels. 

Nuclear power is a very, very dependable form of power, you know it’s going to work.  If you replace it with something like wind power, I think it’s going to be very, very difficult to supply the amount of energy we’re using in this country using just renewable sources.  There’s a professor at Cambridge, David MacKay who worked out that in order to produce all the energy we use in this country using wind power, you'd have to completely cover the whole of the coast with miles of wind turbines to generate that amount of power. 

Nuclear power does have a lot of disadvantages, but it does have the advantage that you know it’s there.  It’s predictable.  You can store the energy.  You're not dependent on foreign sources of energy.  So, if someone stops supplying you with uranium, it’s very easy to store 10 years worth of power. 

Whilst in the long run, it might not be what we want to be using - it depends how dangerous you think radiation is.  If you got a heavily radiated area like Chernobyl, it might not be particularly good for humans, but actually, if you look at things like the amounts of biodiversity there, how well the animals are doing, it’s a lot better than anywhere humans are.  Humans are a lot worse for the environment than radiation is!

There are all sorts of positives and negatives to it.  On balance, I think it’s probably worth using at least until we develop something better.

Ben: - Beverly, I appreciate that we may not have completely turned you into a fan of nuclear but does that help, hearing some of the positive arguments?

Beverly: - It’s certainly interesting to see it that way round.  I think your colleague was not addressing the issue of renewables as much as existing alternatives.  Yes, we’ve got to look at how do we bridge for the next 30 years, and how we use electricity, you know, what sources are we going to use.

Ben: -  Well it’s certainly something that we’ll have to keep an eye on.  Thank you ever so much for your call. 

Ben -  Now that’s a good question.  I think he’s probably referring to the idea that if you stop washing your hair for six weeks or so, then it ends up sort of auto-cleaning and you end up with clean hair despite it not being washed.  I think the truth is a little bit more complicated than that.  It’s not that your hair is clean; it’s that your hair has the right amount of oils. 

Normally, when you wash your hair with shampoo, it’s a detergent and it will strip the oils off your hair.  Hair is supposed to be a bit oily so your hair follicles produce additional oil to make up for the oil that’s been washed away and you end up getting greasy hair.  If you don't wash it away, there seems to be some kind of feedback mechanism that means that the follicles will produce the right amount of oil, and you won't end up with greasy hair.

Now I don't know if this really bears itself out in practice and from what I have seen and read about it, it seems to be much better for people with very short hair.  It’s not that they never wash their hair, it’s just that they don't use soaps or shampoos – they just wash it with water.  The water takes away the dirt and grime but the oils stay there to help protect the hair.  Dave, you've got quite a lot of hair.  How easy is it for you to manage?

Dave -   A while ago, purely in the spirit of scientific inquiry, and much to the annoyance of my then girlfriend, I decided to see what would happen if I didn’t wash my hair for three months.  Basically, what happened is my hair sort of reached an equilibrium.  It was much less greasy than it would be just before you'd wash your hair normally, but still greasier than just after it: a bit greasy, but not very greasy.  So there does seem to be some kind of feedback loop.  Also, interesting things happen when it rained because it appears that your natural grease from your hair is quite good at waterproofing because the outer layer got incredibly greasy and the rain would run off whilst the hair underneath would be entirely dry.  So obviously, natural oils have advantages over conditioners.

Ben - That’s very strange. It's like wearing a natural shower cap made only of hair - that’s revolting.

Chris -   Well, not just spiders but probably many insects can do this.  The example I gave were spiders counting their steps in order to know how to build their webs but also, there was a very elegant paper that’s published in Science a year or so ago by Matthias Wittlinger who’s at Ulm University in Germany.

He and his colleagues were looking at how ants navigate.  Ants use the sun and they also use a compass – they have in their brain a body clock and they're able to use this mental compass of the time of the sun moving across the sky to navigate by.  But they also count their steps and the reason that the scientists know that for sure is that they performed the very delicate task of putting ants on stilts.

They cut hairs off the back of a pig and then glued those hairs onto the ants’ legs to lengthen the ants legs, and when they did this, of course, the ants’ strides became twice as long as they would normally be.  When they followed the ants around, all of the ants overshot their nest because they walked twice as far as they should’ve done.

When they actually, paradoxically, cut the ant’s legs off so they had much shorter legs, they didn’t walk far enough.  They're all circling around, thinking, “Where’s my nest?  I should be there.”  It was clear that they're actually counting the number of steps they've taken in order to find their way around.

In their brain and their nervous system, they must have some kind of neural integrator circuit that, every time they take a step, notches up another 1, 2, 3, and so on, so they can find their way around by counting steps.  So there’s the evidence: ants can do it, it’s likely that other insects probably do the same.

Ben -   So ants on stilts will overshoot their home.  Poor ants.

Dave -   In some senses, it doesn’t actually stop it steaming up.  Steam is lots of little droplets of water.  When the light hits it, the light gets bent and so you get a very distorted image which, when you move away from it, just looks like a kind of mist.  What the shaving foam does: there are lots of detergents in it and those detergents reduce the surface tension of the film of water so it doesn’t form lots of little droplets.  It just forms a big flat sheet that you can see through much better, so you can see through it even though the water is still condensing.

Ben -   So there’s literally the same amount of water there; it’s just a change in the structure of the water.  So why do the droplets make it so hard to see things?

Dave -   Because water has quite a high refractive index - when light hits it, it bends.  If it hits this curved surface of a droplet, each one basically acts as a little tiny lens, light is bounced off in all sorts of different directions and makes it looks essentially white.  This breaks up the image and makes it look misty.

Ben -   Fantastic!  Well very interesting.  Not perhaps what you're supposed to use shaving foam for but if it works, it works.