One of the things Ford Prefect had always found hardest to understand about humans was their habit of continually stating and repeating the very very obvious, as in It’s a nice day, or You’re very tall, or Oh dear you seem to have fallen down a thirty-foot well, are you all right? At first Ford had formed a theory to account for this strange behaviour. If human beings don’t keep exercising their lips, he thought, their mouths probably seize up. After a few months’ consideration and observation he abandoned this theory in favour of a new one. If they don’t keep on exercising their lips, he thought, their brains start working.