Another carbon dioxide question:

When I studied in Germany, there was a time when I lived in a students' dormitory and we had a very small telephone niche on our floor with a door to close in order not to disturb other students by loud talking.

Once after about half an hour of vivid talking with the door closed I felt as if I was going to faint.

I think the air volume in there was only about half as big as in a normal phone booth (their outer measures are 100x100x220 cm in Germany), but the door was less tight.

But I also know that "feeling as if" and really fainting are a long way from each other. I think there are no cases reported of sobre people fainting in phone booths.

How long can one remain concious with, say, two cubic metres of air? Or with one? Or do they have some secret airing system in there?

(good thing everyone has mobile phones now)

I have been told sucking on charcoal will mean that you can always give a positive sample on a breathalyser, no matter how much you drink. Is this true, and if it is, how does it work? If it isn't, would anything work?

It seems that breathing can't be distracting my concentration, and nothing should be able to make me "forget" breathing, since I breathe all right while sleeping.

Nonetheless, when I am doing something difficult and important, for the few most tricky moments I tend to hold my breath (and become aware of that only afterwards). Why so? I should think it's better for performing the task to have enough oxygen in the brain?

I have just read that a Swiss man, Peter Colat, has set a new world record for holding his breath under water: 19 minutes and 21 seconds. How is this possible?

John Junior, Leicester, UK

Is the part of the brain that controls automatic breathing and the part of the brain that stores memories the same or are they somehow connected? If you interrupt your breathing rate and recall a memory do you activate a certain part of the brain that handles both breathing rate and memories?

I have attended several different types of exercise class over the years, and I'm always instructed to breathe in through the nose and out through the mouth while exercising. No instructor can tell me why.

Is there a scientific reason for this advice?

Heather Shute, Oxfordshire, UK