Kat - Foot odour is primarily due to the bacteria that live just around your feet. If you've got sweaty feet, if you don't keep them clean you're going to have a massive build-up of bacteria. Technically if you rubbed your feet you would transfer the bacteria but then they would need to have the right conditions like sweaty, dirty feet. One thing that can make your feet smell a bit is having athlete's foot. That is a fungal infection and you can catch that. You can pick it up in changing rooms, you can pick it up by rubbing your feet against someone's who's got it. That might make your feet a bit whiffy and you could catch that.

Dave - Would different bacteria smell different? Maybe you can catch a different set of smelly bacteria off someone else?

Kat - Different bacteria do have different smells. There's all kinds of bacteria in the world that have different properties and it's all about the gases that they produce that make you smell. They may react differently on your skin if you have different levels of things in your sweat. I don't want to talk about this any longer!

Chris - A few foot-related facts. Your feet actually squirt a litre-and-a-half of sweat into your socks every 24 hours. You're shedding something like 40,000 skin cells every minute or so over a lifetime that adds up to one-and-a-half stone of dead skin. If you take the surface area of your body and feet are a proportion, that's a lot of dead skin just off your feet. If your feet are stewing in a nice sweaty pair of trainers that don't allow them to breathe what you've got is bacteria, warm, wet and food and that's what causes the bacterial banquet that makes the smelliness.

Kat - Wash your feet, change your socks.

Kat - That's my idea of fun. I don't know because if you have a bath...

Chris - If you drink the bath water...My children do!

Kat - If you drank it, it might. I don't know if we absorb stuff through our skin. I thin kthe skin's barricaded for the blood stream.

Chris - The skin is pretty good but you do absorb alcohol at the sites of mucus membranes. That's why French people love putting suppositories in their bottoms, for example. There are some tablets you can put under your tongue. Where you have a mucus membrane the blood vessels are very close to the surface and the skin Is very thin. You can get things that dissolve well in fats to go through.

Kat - Would a lady, as well – through her lady parts – could get drunk by sitting in a bath of vodka?

Chris - Yes, men as well. I think you probably could absorb small amounts that way. Also your eyes, you cold get some of the vapour going in through your eyes, up your nose because it would volatilise. Presumably you'd make it warm sitting in a bath. You'd probably want it warm.

Kat - Maybe a cocktail umbrella.

Chris - Maybe some fruit to go with it.

Dave - I guess it'd also dry you out very quickly because osmosis would suck al the water out from inside you.

Chris - You'd be quite dessicated. You wouldn't want to drink the vodka probably, afterwards.

Chris - I can probably help you out there. Yes, morning sickness is because by definition it's genetic. When you're pregnant you've got someone else's DNA in you and as a result it makes you get sick. Everyone gets it, pretty much, once or twice in your lifetime – depending on how many times you get pregnant. Therefore you could say it is inherited. What actually is it? This is emesis gravidarum which is a fancy Latin expression which means 'puking of people who are pregnant.' Why this happens is we think it's down to a hormone called beta-hCG: human chorionic gonadotropin. This is a hormone which is produced by the early foetus, just as it's beginning to implant into the uterus. It puts this into the bloodstream to maintain the survival of a structure called the corpus luteum which is where the egg came from in the ovary. That structure makes progesterone. Progesterone keeps the uterus lush and well-supplied with blood so it can sustain a pregnancy. Until the placenta develops properly which is where the progesterone comes from afterwards you need that corpus luteum to stay alive. That's where you make beta-hCG. But it seems to mimic another hormone called TSH: thyroid stimulating hormone. When women are pregnant they seem to have a slightly higher metabolic rate. It might be that part of the symptoms are your metabolic rate going up because you have more active thyroxine, the body's own thermostatic hormone. As a result of that extra thyroxine level you are made to feel as if you are being sick more often. Usually though, it's not major problem., It comes on at 2 months of pregnancy, it peaks at 3 months and is gone by 3 or 4 months. There are some people who are very unfortunate and they have hyper-emesis and this can necessitate hospitalisation, unfortunately because it can be so severe. There is some evidence that can run in families but I think the numbers are so small there's not been any really strong, robust evidence to actually confirm that.

Dave - Well when any bomb explodes the first thing you're going to get is a lot of high-pressure gas because you've taken a load of solid and turned it into gas. It wants to expand. Water isn't going to move away nearly as quickly as air does. The pressure's going to remain very high, pushing water away. The fastest the water can move away is roughly the speed of sound in water. That's 1400m/s. You're going to form a bubble. As that water is pushed away very fast you're going to get a second powerful sound wave or pressure wave moving away from it. If the water doesn't compress that's going to have a very high pressure and do a lot of damage which is why depth charges can destroy strong things like submarines, even 10-20m away. Apparently it's way that there's a theory of how you might be able to blow up safes. If you fill a safe with water an drop a small charge in then because the pressure change is so much greater it might blow the door off.

Chris - That's because all the pressure is being exerted on the safe. If you were to just stack a load or dynamite at the front of the safe, some of it would hit the safe but a lot of that pressure would go out.

Dave - The gas that's produced, all that extra volume that's produced is pushed on the side of the safe. Normally you can just compress the air inside the room.

Kat - It would be more explosive if you fart in the bath as well.

Chris - Absolutely, the bacteria that live in our mouths and metabolise what we put into our mouths and their metabolites are smelly. They can also be helpful because scientists showed in the last six months that they also give certain wines that lovely, what's called, retro aroma. The taste of the wine coming on in your mouth after you've swallowed it. Scientists showed that the bacteria break down sulphur compounds that are previously flavourless. As soon as you put them in your mouth the bacteria break down the compounds into smelly, whiffy compounds and that gives you the extra taste and extra dimension to a fine wine.

Chris - I reckon the answer is probably yes. What do we think?

Kat - Yes. Evolution, natural selection is basically the response of organisms to changes in their environment. Our environment is changing. We are adapting. We've grown in size a lot due to better nutrition over the past 100,000 years.

Chris - Yes, I think I'd probably add to that and say there are good examples of things like sickle cell anaemia where people have evolved this trait which makes your haemoglobin a funny shape which means it's not so good if you have two copies of that gene. If you have one copy you can't catch malaria. That's a good example of a mutation that benefits you in Europe. Lactose intolerance is absent but it's present in other populations in the world. We have evolved a gene in Europe which enables us to digest lactose, a major sugar in milk because people began to farm cows. There's another mutation that makes us healthier.

Kat - They say the genes for very fair hair and red headed are dying out because of inbreeding. We are evolving that way.

Chris - And also resistance to HIV, there's CCR5-delta-32. This is an alternative form of a gene in the immune system which happens to give you, if you're a carrier of that, resistance to HIV infection. This has only really surfaced as important since HIV came along. There's a couple of us gaining a new mutation.

Dave - Although I guess in Western countries where pretty much everybody survives the only real survival of the fittest is to do with how many children you have. The direction in which the western population is evolving is towards the people who have the most children.

Kat - It's the breeders!

Chris - It's a good question. Why haven't we evolved out of getting diseases like arthritis? Why hasn't that gone away, why hasn't evolution given us better cartilage. The answer is, Dave kind of hinted at this earlier. It's all down to having children. If something stops you ahving children then the genes that stop you having children will be removed from the population and genes that help you to have children and live long enough to have children will be enriched in the population. Since arthritis is really a disease of old age – it doesn't tend to come on until you're in your 60s. I think 100% of people aged 60 have some degree of arthritis. It's not till you're a bit older than that even that you tend to have occupational problems of joint damage already that you need major surgery. The reality is that because arthritis doesn't stop you have you children the genes that might make you have an increased risk of it don't get removed from the population. As a result we all have the same risk of arthritis. It's a bit like going bald. Because most people don't get bald until after they've had children as a result we haven't removed that gene from the population. There's lots of men who've got male pattern baldness.

Chris - The reason for that is because you have various reflexes that are designed to protect your airway. There's a nerve supply, the internal laryngeal nerve which is sensitive to everything touching your epiglottis inwards and down into your airway. You need to defend your airway very carefully because if anything goes in there it could threaten your ability to breathe. There's a very profound choking reflex and that triggers a cough. It also triggers various secretions to happen, the idea being that it will lubricate your mouth and anything that's stuck will get free. At the same time the same secretery, motor system also make your eyes water a bit. It makes tears come to your eyes and also what you're doing when you're coughing and choking you're blowing air up your tear duct. Normally the tears that you've got in your eyes drain down little punctum which is a little plug hole in your lower eyelid towards the middle. They go down towards the naso-lacrymal duct and tip into your nose. If you raise the pressure in your nose by coughing, sneezing, blowing your nose the pressure is reversed. It pushes the tears back up your tear duct and into your eye. There's two things going on. One – you increase the secretions and two you probably jettison some tears back into your eyes.

Dave - We were looking it up – they were about 1/10^th of a millimetre high. That would come to 100,000km high or a third of the way to the moon.