That's a really good observation. When oil is put on water, it floats. However, when it floats, it doesn't form globules like soap; it spreads out as thinly as possible. This creates a layer of oil so thin in some places that it's as thin as the wavelength of light that's enabling you to see the oil. However in other places, it's slightly thicker When light goes towards the oil and tries to get through, some of the light gets reflected back by the layers of oil before it hits the water. The oil is acting a bit like a mirror on top of the water. Because the oil is thicker in some places than others, the light that is reflected back into your eye has had to travel further in some places than others. The light is split into different wavelengths and gives you pretty patterns.

When you have surgery, the surgeon has to cut through the skin. In the process of cutting through the skin, they will almost certainly cut through some nerves. Scientists have now come round to thinking that itching is caused by a special class of nerve fibre that seems to convey the sensation of itchiness. The reason that scars and scabs itch so much is perhaps that when these tiny nerves try to re-grow, it's possible that they sometimes fire off inappropriately and fool the brain into thinking that there's an itch there when in reality there isn't. Another possibility is that when the tissue is putting itself back together when you have a scar, then you get lots of tension and funny pulling within the skin. It's possible that this may be triggering off the itch sensitive nerves as well.

There are lots of ways in which the brain can be damaged. Sometimes the brain is born incorrectly, so it might have some of the special genes that make up the brain missing. This would make the brain damaged from the outset. Unfortunately, some babies are born with brain damage if their mum has difficulties during labour and the brain doesn't get enough oxygen. As I said earlier, if a baby is born very prematurely before their brain is properly formed, that can also lead to brain damage. There are lots of adult diseases such as Alzheimer's and Parkinson's disease which will damage and kill off the brain cells. Largely speaking, many of these brain cells cannot be repaired. Perhaps one of the most common forms of brain damage, and let's not forget that your brain also includes your spinal cord, are accidents. Unfortunately, many people who have bad accidents or falls will damage part of their back, spine or brain. Sadly, it's something that we can't cure at the moment.

I'm pleased to tell you that you're right and your friend is wrong. The skin is actually classed as an organ as it performs a function in its own right and has specialised tissues to do it. I hope for your friend's sake that there wasn't too much riding on the bet!

That's an extremely good question. The brain is a funny organ because it's made up of lots of different cell types. Some of these are brain cells and some of them aren't. What do I mean by this? Well, you have blood vessels in your brain, specialised cells that mop us damage and infection, and if you damage your brain, the non-brain cells in your brain actually repair themselves very quickly. The problem is that most of the really important brain cells that carry signals and tell your limbs how to move, your brain how to think and your body how to behave, unfortunately repair very slowly, if at all. That's why we've been working on a very special population of cells called stem cells. We hope that these cells have two very special properties. One is that you can grow them for a very long time in a dish in a laboratory. This will let us take a few cells out and grow them up into as many as we need. The second thing is that we want to be able to coax them into becoming brain cells. Hopefully you can inject them into people with brain damage and repair the damage. Of course, at the moment this is very early days and it's very experimental. However, some of the results we have at the moment from these early experiments are very exciting, and we hope that in many years' time, it will lead to a treatment for people with brain damage.

The sun is so hot because the sun is a giant nuclear reactor in the sky. It's mixing on hydrogen with another hydrogen to make another light gas called helium. You can find helium in the funky balloons that float. When you mix the two hydrogens together, you get a lot of heat energy, and so the sun on its surface is at least six thousand degrees centigrade. That's what keeps us warm.