If you drink milk that isn't skimmed, it's got lots and lots of fat in it. Having lots of fat isn't good for you because of the calories, but also because it furs up your blood vessels. Milk is also very rich in calcium which, in people who are prone to stones, can deposit in the kidney and cause kidney stones. And the other side effect of milk that not many people know, is if you have irritation to the stomach lining and you're at risk of getting stomach ulcers, calcium is used as a co-signal by the wall of the stomach to produce acid. If you have calcium levels in the blood going up, you make more acid. Some people think when they have a dodgy stomach that drinking milk will settle it. When you first do that your stomach feels happier because you've given the acid something to eat other than the wall of your stomach. But then the calcium is absorbed and goes into the blood stream and increases the amount of acid your stomach makes, causing a vicious cycle.

No-one knows precisely why this is, but people think that it is a form of referred pain. Referred pain means that you have damage or pain coming from somewhere in your body but you feel it somewhere else. People who have a heart attack often report feeling pain in their neck or in their left arm - not where their heart is. So in the same way as that, you've got your nervous system fooled into thinking that the pain's coming from somewhere else. What scientists think is that the nerves in the mouth that are very sensitive to cold temperature accidentally trigger the nerves supplying the front of your head. It then thinks that there's a painful stimulus coming from there, when it's actually coming from your mouth. Another possibility is that when you put very cold things into your mouth, there's a nerve reflex to do with regulating heat and blood flow through your face and head. It might be that when you put something cold onto the nerves that signal this reflex, it goes into overdrive and the blood vessels temporarily open too much because they think your head is freezing cold. In the same way that a migraine will give you that horrible throbbing headache, perhaps that's why you get that temporary pain right at the front of your head.

[We put this question to David Thomas, author of ‘Surviving Antarctica’]

Because your eyeball is contained within your head, and your head is kept at body temperature, it never gets cold enough to freeze.  The eyeballs in a dead body would indeed freeze, but while you’re alive and radiating heat it can’t.  Even tears wont freeze immediately, as they are very salty, and salt reduces the freezing point.

This is similar to a question we had a few weeks ago when we were asked why it is that when a can of fizzy drink falls out of the dispenser, it doesn't explode when you open it. Dave and I discussed it and thought that when the can falls, it tends to spin. It lands on its side with the liquid spinning in a circle inside the can rather than striking the top of the can. Because the inside of the can is very smooth, the fluid doesn't come into contact with many rough surfaces and so there is nowhere for the gas to nucleate and form tiny bubbles. What could be going on in the beer bottle is that once the bottle is open, there is no pressure inside. The gas dissolved in the beer wants to come out as bobbles. If you smash the top of the bottle with another bottle, it makes a shock wave and I think that that would be sufficient to start some nucleation inside the drink. Once you have one bubble, it provides a site for other bubbles to form on. The whole thing feeds back on itself. As the bottle has a narrow neck, as soon as you have some bubbles it fills up and suddenly doesn't have anywhere to expand to. This pushes everything out in a massive volcano.

The way your voice works is that your vocal chords vibrate and make a series of different frequencies. Your throat and mouth act as a resonant cavity. This is a bit like a tray of water, you can vibrate it at lots of different frequencies and not much will happen, but if you vibrate it at the same speed as a wave will travel up and down it, the wave will get stronger and stronger. Similarly if you vibrate your throat at the right speed the vibration will get stronger and stronger so you throat will amplify some of the frequencies your vocal chords are making (by changing the shape of your mouth you can alter which ones are strengthened which is how you make different vowel sounds). Sound travels faster in helium so the vibrations will get from your vocal chords to your mouth quicker so your throat will resonate at a higher frequency and hence a higher pitch.

WARNING - There is no oxygen in a helium balloon and your body has no way of detecting that it is short on oxygen so you will feel fine until you fall unconconcious. So it is recommended you don't try and replicate this. If you must have a go, don't take deep breaths of helium or more than one breath of helium every few minutes.

I understand the point you're making and it's a good one. You're half right and half not right and the reason is as follows: the north pole is ice that's already floating. If that melts, you're quite right, it's never going to overflow because when it melts it will displace an equal volume of water as itself. As it's made of water it will just turn into water and never overflow. But here's the spanner in the works: Greenland for example and Antarctica are continents and there's land under there. The ice is not under water but sitting on land, so if that melts it's going to raise sea levels drastically. In fact there's enough ice locked up in Antarctica and Greenland to give us about 7 - 70 metres of sea level rise. There's a paper that was published in this week's edition of the journal Nature in which scientists have used two satellites in space. It's called GRACE but should be called BRACE because they work in concert with each other, and they work out how much mass there is on Earth underneath them by working out how fast one is accelerating because of gravity compared with the other one. What they've done is to watch Greenland for the last two years and they've found that Greenland has lost 248 cubic kilometres, plus or minus about 60, of water every single year in the past two to four years. It's gone up 250%, so it's a scary amount. That is enough to raise sea levels every single year by about 0.5 millimetres. That's Greenland on its own in one year. So if things really do take off with global warming, we're in trouble.