From the end of Through the Looking-Glass, by Lewis Carroll [pseudonym of mathematician Charles Lutwidge Dodgson (1832–1898)]:
It is a very inconvenient habit of kittens (Alice had once made the remark) that, whatever you say to them, they ALWAYS purr. ‘If they would only purr for “yes” and mew for “no,” or any rule of that sort,’ she had said, ‘so that one could keep up a conversation! But how CAN you talk with a person if they always say the same thing?’

On this occasion the kitten only purred: and it was impossible to guess whether it meant ‘yes’ or ‘no.’