One of the things Ford Prefect had always found hardest to understand
about human beings 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.