A joke is not a thing but a process, a trick you play on the listener's mind. You start him off toward a plausible goal, and then by a sudden twist you land him nowhere at all or just where he didn't expect to go.
They took their meals together; and it was remarked on such occasions, when the friendship of animals is put to a hard test, that they never quarrelled or disputed the possession of a favourite fruit with each other.