At first, Ford had formed a theory to account for this rather strange behaviour.

4 seconds sound clip from The Hitchhiker's Guide to the Galaxy (1981) - Episode 6 sitcom.

You can hear this line at 00:07:16.820 in the Blu-ray version of the TV Series.

Quote context

[...]

- How?

- Quiet. We're thinking.

- So, this is it? We're going to die?

- I wish you'd stop saying that.

- One of the things that Ford Prefect had always found hardest to understand about human beings, was their habit of continually stating and restating the very, very obvious, as in, 'It's a nice day. ' Or, 'You're very tall.'

- Or, 'So this is it, we 're going to die. '

- At first, Ford had formed a theory to account for this rather strange behaviour.

- 'If human beings don't keep exercising their lips, he thought, their mouths probably seize up. '

- After a while, he abandoned this theory in favour of a new one.

- 'If they don't keep exercising their lips, he thought, their brains start working.'

- In fact, this second theory is more literally true of the Belcerebon people of Kakrafoon Kappa.

[...]