Mucus is very important, especially in your lungs. We did an experiment with this on TV a while ago. Mucus catches all the dust and bits in the air. If you didn't have mucus, all the tiny bits in the air would be carried deep into your lungs, which can do all sorts of damage, especially if it's toxic. As the mucus is sticky, it catches all these bits and you can either bring it up as phlegm or it runs out of your nose, taking all the poisonous nasty stuff with it. The reason that Dee probably has this problem could be down to allergy or some other inflammatory process going on. But usually it's down to something that you're breathing in that's making your airways inflamed. The reaction to an inflammation is to make lots of mucus. How do you get rid of it? Well there's one way to knock it down, which is to take some steroids like you've done. That will help to stop the inflammation quite effectively. The other way is to take some antihistamines. These are good because they stop histamine, which is a class of cells produced by mast cells. Mast cells are coated with an antibody called IgE that recognises allergy-provoking substances. When the allergy-provoking substance binds onto the IgE on the mast cell, it tells the mast cell to pump out this histamine, which is an inflammatory substance that makes you have sticky eyes, itchy eyes and a blocked up nose. If you take antihistamines then you block the action of the histamine before it has a chance to get going.

Magnets are very useful things: you can stick things to fridges with them and they're very important in things like hard disk drives in your computer. You can even make levitating trains with them. But how do you make a magnet? Inside a metal like iron there are lots of tiny little magnets, but to start off with they're all pointing in different directions. It's like if you had a load of magnets inside a big bucket: they'd all be pointing in a random way. What you need to do to make it into a magnet is to line up all those tiny magnets. The way you do it is to heat up the material, which allows all the mini magnets to move around. You then put a big electric field around it. This causes all the little magnets to line up, as you may have seen compasses do in a magnetic field. If you then cool it down in that magnetic field they'll all be lined up and you'll have what you think of as a magnet. Of the elements in the periodic table iron, nickel and colbolt can be made into magnets. But you can also make alloys that make much stronger magnets. To make a very strong magnet you need something that will make the tiny magnets stay in the right orientation after it's been cooled.

It's not actually getting any smaller yet but it's stopped getting any bigger, which kind of amounts to the same thing. What we see is a lag between the CFCs or chlorofluorocarbons, which are implicated in causing the ozone hole, going into the atmosphere. Then they react over Antarctica and damage ozone and make the hole bigger. If you see the hole not getting any bigger then that means that the reaction causing it must be slowing down, and at the same time ozone's continuously being remade. So the two processes must now be in balance, meaning that if it keeps on slowing down, within the next few years the hole should start to shrink a little bit. But let's not be too over-confident or complacent about this because the ozone hole is about the size of the American continent.

The way a cassette works in the first place is that you have a big long strip of iron and when you apply a magnetic field to it, it gets magnetised. That's how you record things onto it. The varying magnetisation can then be converted into vibrations and you hear that as sound. The way that a double-sided cassette works is that when it's one way up it reads information from the bottom of the cassette and when you turn it over it reads it from the top of the cassette. So you have two strips: one at the top and one at the bottom with different information on it. So what's probably happening when you're hearing the muffled sounds is maybe the sensor that's reading the magnetic field is a bit too close to the middle and so you're picking up some of the other side of the tape, probably backwards.

The reason it's red is because it's got iron in it. If you look down a microscope at blood, what you'll see are thousands of tiny little red cells that are referred to as looking like concave discs. If you look at them from the side, they look like a number eight and that's because they've got a thick ring round the edge and a flattened centre, a bit like a doughnut. They're crammed with a substance called haemoglobin, and haemoglobin is that stuff that carries oxygen around the body. It's a protein - in fact it's four proteins stuck together. In the centre of those four proteins there is an iron ion. Because it's got iron in there it's the colour red. Now lots of animals have a different version of that protein. For instance, the horseshoe crab has blue blood because they use copper instead of iron. The real hippies of the haemoglobin world are a kind of annelid worm that lives in the sea. It actually has blood that's purple when it's oxygenated.

I've picked some up by wading in streams occasionally. If you wade around then they should find you! Medical companies do actually supply and you can use them for medical purposes. In the old days people used to blood let because they thought that it was good for people. But in fact leeches are very useful because they have venom that stops clotting. It's called hirudin and it's a tiny protein. When they bite you they inject it and it keeps the blood from clotting so they can keep drinking. Surgeons love them because if you have a bit of plastic surgery when a part of your body has been severed such as a finger or piece of ear, it's very easy to reattach things like arteries because they're quite large and chunky. But the veins are quite floppy, difficult to identify and it's very difficult to reconnect them, so blood can get into your tissue quite easily but not back out again. This means that the tissue can end up starving because the circulation can't go all the way through. So what scientists and doctors have found is that if they attach leeches around the site where you want to stitch something back together, you can keep pulling to blood out. As long as you keep a nice flow of blood coming in, then the tissue revitalises and the vessels grow back together. When the leech gets full, it just drops off. There are companies that will supply medicinal leeches but they're usually used by doctors, not members of the general public.

With glasses, there's definitely some kind of environmental effect there. If you spend all your life studying, then you're much more likely to end up with short sightedness. I can see that both Phil and I have glasses on today! In Singapore where there's a very strong emphasis on education from a very early age and lots of people spend lots of time studying, the rates of short sightedness have gone through the roof. There's a lot to be said for people going out onto the sports field and learning to focus their vision in the distance. When you're young and you're body is developing and growing, if you do a lot of close work you don't develop a capacity to see well into the distance. But in terms of degeneration, just because you wear glasses doesn't mean that your eyes are actually degenerating; it just means that they're not working as effectively as they could. With going deaf, on the other hand, there's actually a problem with part of the ear that turns sound waves into electrical signals. That's because over time the tiny nerve cells that do that job get damaged by loud noises, the effects of ageing and the effects of damaging chemicals in the blood stream. Once they're lost, you can't replace them, which is why you get a progressive deafness.

I think that polar bears are a lot faster than hippos, so that element of nimbleness would give it a great advantage. Although I guess if they got close enough, a hippo is a really vicious animal. I think that more people are killed by hippos in Africa than they are by lions and tigers and actual carnivores.

That is called the photic sneeze reflex and it's something that's a big problem for people who want to be in the RAF or in the US flying corps. One in four people has this, it's thought to be genetic and it tends to run in families. It's seems to be that when you have bright light going into your eyes, in those people who are susceptible, the light in some way triggers you to want to sneeze. We used to think that the light made your eyes water and the water ran down your nose, making it tickle. But it happens far too quickly for that so we think that it's actually some mis-wiring in the back of the brain that triggers your sneezing centre.