The ears are indeed connected to the back of your throat by a very narrow tube called the Eustachian tube. It goes from the area just behind your nose, so where the nose joins the back of your mouth, out to your ears. But it goes to the bit of your ear on the inside of your ear drum, not on the outside. The outside of your ear canal, the bit where you can stick your finger in and wiggle it up and down, that ends in your ear drum. This forms a solid layer which separates your external auditory canal, which is the bit you put your finger in, from the inside of your ear. That means that there is no way for water to get in there at all. If you do get water in your ears, it's because some water has got up your nose and trickled down this very fine Eustachian tube and got into your ear. You might then want to know why your ears go pop when you go up in an aeroplane. The reason for that is because the Eustachian tube is quite narrow, the pressure pushing on the outside of your ear compresses the air on the inside of your ear by squashing the ear drum. The idea of the Eustachian tube is to let it equilibrate. If you have a cold or a nasty infection in the sinuses, it can block off the Eustachian tube with some mucus. That mucus can stop the air pressure equilibrating, and that's why you have that funny popping sensation. You can equalise it if you hold your nose and blow hard against it. This forces air into your ear and helps to equalise the pressure. But there is no connection between the outside world across your ear drum.

Yes, it is. Part of the reason is that when you yawn, you squeeze you eyes tightly shut. The way that tears flow is that they come out of you lacrimal gland which is on the upper outer side of the top of your eye. They then flow in a film across your eye obliquely downwards and inwards. The tiny black dot on your lower eyelid is called a punctum, and that's where your tear duct starts. If you squeeze your eyelids tightly shut, you stop the tears flowing across your eye and into the tear duct and so they have to come out. This makes you cry a little bit, which is why tears come out when you yawn.

Actually very few diseases are transmitted by insects and their relatives. But when it comes to the impact overall, they're perhaps just as good at transmitting diseases as people coughing and sneezing. If you look at the number of cases of malaria each year, and we're talking about tens of millions, we get about two million people die of malaria each year in sub-Saharan Africa. The population at risk is several hundreds of millions, so the chances of getting a disease from an insect are much higher in certain parts of the world, even though the variety is very small. To be a virus transmitted by an insect, you have to be a very special type of creature in that you have to be able to survive going into the insect's gut and pass through into its blood and travel to the salivary glands. It then has to survive transferring back into the human. HIV just can't do that, but malaria can.

The life cycle of the louse is very distinct and discreet in that the eggs take seven days to hatch, and that's almost invariable. Up until that time, you're not going to get rid of all the little ones that are going to hatch out. But it takes them nearly ten days to become adults, and so therefore they can't lay any eggs until they've reached that point. In between those two points, you have a stage where the lice won't move into anybody else. While they're half-grown, they stay put. It's only when they get to about 6 or seven days old that they start getting interested in moving house. From then on, they'll start shifting onto somebody else. Your lady wouldn't have been infectious if she only had baby ones on her.

The reason is that it's just a reflex. Because your body has to generate a huge rush of air to make you sneeze, everything clenches up tight to make you go atchoo!, and blow air out of all the right holes to clear the mucus. Part of that is to blow air the wrong way up your tear ducts, which is why your eyes water when you sneeze. You do screw up all your muscles to make sure you don't hurt your eyes, so it is sort of protective. Contrary to myth your eyeballs won't pop out if you sneeze with your eyes open.

When I was young this was a very common practice, however, chicken pox can actually be a very dangerous disease, in pregnant women in particular. If they haven't had chicken pox and get it early in pregnancy, it can cause problems in the baby, so they need to see a GP very quickly. Equally if adults get chicken pox, again, there's a much higher rate of complications with swelling of the brain and pneumonia. Every year in Cambridge we have one or two people who die from chicken pox. It's more serious than people think. So it's not really that great to get it, even if you're young because you can always pass it onto someone else, who might be pregnant or older. The next thing coming along is a chicken pox vaccine, which may well be in use in a few years time.

Only cat fleas. Some rodent fleas will bite us but won't actually survive to lay eggs.