Normality.

To show that you are no longer mad, Papillon was advised as he tried to devise a way to get out of the prison hospital, make sure that eight out of every ten things you say are sensible.

Implicit in this remark, then, is the suggestion that there are degrees of normality, straying beyond the boundaries of which promotes suspicion or unease. It is an obvious point, but one worth pursuing.

I mentioned before that I sometimes log onto chatrooms with a view to tricking humans that I am a computer, in a kind of miniature reverse-Turing test. Perfect spelling is one such way of perpetuating the myth - a single error is enough to convince an alert-enough person that it's one of their own playing mind-games. Similarly, too many spelling mistakes, and the conclusion is that we are dealing with a child or a madman or a joker.

We carefully negotiate the boundaries, then, between computer-like perfection and being one of the 999,999 inaccurate monkeys hammering away at a typewriter. Is it correct, though, to say that we 'negotiate' it, that there is some kind of conscious thought going into most of the things we do on an everyday basis?

When I walk, there is no sense of pausing to work out how to put one foot in front of the other; only sometimes do I struggle to think of the appropriate word which is 'on the tip of my tongue.' It is all done in a natural sequence, divorced from attention or concentration.

Non-verbal statements, though, I find more difficult - and indeed I do need to devote a second or two to selecting the appropriate one from the almost-inexhaustive list. Is this the right time to smile? Is this the right time to make a non-commital grunt? Is this the right time to shrug in resignation?

Such instinctive creases of the face, bovine lowing and kinetic tics should not require prolonged deliberation - but I find that they do, because I am more often than not incapable of feeling, or of even registering any interest. Pausing momentarily, with a face on standby, to choose the correct expression, causes other people to think of Papillon's eight-out-of-ten advice: he's having to think what to look like, and therefore he is mad.