I'm pretty sure that what they work with is sodium acetate. What you've got is a super-saturated solution of sodium acetate, and as this begins to crystallise, it gives off a constant heat of about 55 degrees centigrade, which is a nice comfortable temperature for something like a hand warmer. Now how do you get this to work? Well as you bend the metal, I think you create surfaces that are like the crystals that could be formed from the solution. Once you've done this, you're really seeding the crystals, and so one forms and then another and another until it spreads throughout the bulk of the hand warmer. All the time it is giving off this heat. Eventually, the heat will stop because you've crystallised the whole thing. You can repeat the whole process by putting the used hand warmer in something like and oven, until the crystal is all melted again.

A sneeze is a bit like an itch in your nose. When you have an itch, it's extremely pleasurable to scratch it. Unless you have really long fingers, it's not that easy to scratch that far up your nose! So what sneezes do is use air to perform a metaphorical scratch. What we know about itching is that there is a special class of very small nerve fibres, and they signal itchiness. In fact, you can switch off the signals into the spinal cord and brain for itchiness if you cause a little bit of pain. That's why scratching an itch actually helps to relieve an itch, because you cause a little bit of pain and it switches off the itch signal. In sneezing, you get that pleasant relief because you've got rid of the itchy sensation, and also dislodged some of the gunge that's in your sinuses.

The reason that you get a rainbow, is that sunlight shines into a raindrop. Raindrops are very tiny and the surface of it is like a mirror. As the light waves go into a raindrop, they hit the mirror like surface and reflect. The light bounces off the back inside surface of the raindrop and comes back out of the front. Now if you've ever seen a prism, what that does is split white light into all the colours of the rainbow. White light is actually a mixture of lots of different colours. When the light comes back out of the front of the raindrop, it splits up into all the different colours of white light, and that's how you get a rainbow.

This is a Nobel Prize winning level of question, and if either of us could answer that, we'd probably be straight of to Scandinavia! The easy answer is, have you noticed that men tend to put weight on round their middle, and women tend to put it on round their bum? So there has to be a genetic component to this. The old saying goes that women have lots of fat around their hips and bums because that's their store for pregnancy. However, we don't know exactly why and how the body decides on the distribution of fat in the body. What we do know is that you can lose weight from those areas just as easily as you can anywhere else, if you resort to the right kind of exercise regimen. Energy in equals energy out, plus or minus any weight gain. So if you're not burning up the energy that you're putting into your body, the energy has to go somewhere. You body thinks that the most efficient way to store it is as fat, which it puts under the skin, or if, a man, as a bit of a beer belly.

It's luminol that you're activating. It's a chemical that things like glow worms produce. You can carry it around but to make it glow you need to activate it. What we usually use to activate it is hydrogen peroxide. When you snap a glow stick, it allows the two chemicals to mix together and causes a chemical reaction. The reaction won't last forever, but you can get to do what flies can do naturally.