Questions and answers provided by Science Line's Dial-a-Scientist on 0345 600444

Q What happens to waste from aeroplane toilets?

A It's a myth that it can leak out and fall to the ground in huge frozen blocks. Waste on aircraft is stored in tanks, which are pumped out later on the ground. The bits of ice which can fall from a plane generally come from the wings, where ice accumulates from water vapour in the clouds.

Q How do they put stripes in toothpaste?

A Basic toothpaste is white. Coloured gels are then made in separate steel mixers, and each colour is piped to a specially designed nozzle which keeps the colours separate as they are pumped into the tubes - which are filled from the bottom up at a rate of about 250 per minute, and sealed. The stripes are carefully formulated to be stiff enough not to flow into a single messy mix, yet soft enough to be squeezed out of the nozzle. Because each tube is filled to capacity, the colours can't normally mix up.

Q Why do we crave chocolate?

A Chocolate contains large amounts of phenylethylamine, which is also present in our bodies and released during sexual arousal, heightening sensation and raising the heart rate. It also contains methylxantine and theobromine, which have similar effects to caffeine. And if that isn't enough, it is solid at room temperature but melts at just below body temperature - that is, in your mouth.

Q Where do comets come from?

A Comets are made up of rock and ice left over from the time when the solar system was formed. Dutch astronomer Jan Oort suggested in 1950 the existence of a cloud of comets 50,000 times as far away from the sun as is the Earth. The Oort Cloud is thought to contain about 100 billion comets, some of which can get nudged out by gravitational interactions with passing stars and then fall into closer, elliptical orbits about the sun. Other comets may also come from the Kuiper Belt, which is closer to the Earth than the Oort Cloud but contains smaller objects.

Q What is the funny bone?

A The funny bone is actually a nerve which runs through a groove in a bone very close to the surface of your skin. It's called the ulnar nerve because it runs through the ulna, the outer of the two bones of the forearm. The ulnar nerve provides sensations for the wrist and hand. At the elbow, the ulna sticks out, and both it and the ulnar nerve are very close to the skin, making them easy to bump or knock. If the nerve itself is hit, you get a very painful physical reaction, and when things hurt a lot, you get very emotional, which means you laugh (or cry, or both) a lot.

Q How does a lie detector work?

A Lie detectors work on the principle that anyone who's lying will be nervous, and nervous people tend to produce more adrenaline, which makes their hearts beat faster, their skin temperature rise and makes them sweat more. A lie detector basically measures how these things change during questioning. However, people generally get nervous anyway if they're being questioned, while some people can control their heart rate if they concentrate. So, lie detectors aren't foolproof indicators of guilt.

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