Laughter is a sort of knight's-move; our discourse proceeds in linear and logical ways, like pawns and queens in motion. But a joke leaps and slips to the left: a man goes into a library and says "can I have fish and chips please?" And the library says: "but ... this is a library!" And the man says: "Oh! Sorry. [whispers] Can I have fish and chips please?" A little slide into left-field at the end, and we're there.
This knight's-move argument is hardly original, mind, as a way of talking about laughter. But what it makes me think is: why don't I laugh, when playing chess, at the movement of knights? Am I missing the joke? What does this say about my sense of humour?