Unseen Academicals (Discworld, #37; Rincewind, #8)

by Terry Pratchett

‘Oh, that’s crabs for you,’ said Verity, disentangling the ones who had hitched a ride. ‘Thick as planks, the lot of them. That’s why you can keep them in a bucket without a lid. Any that tries to get out gets pulled back. Yes, as thick as planks.’