 This joke has been used by comedians for years as a mental  stretching exercise. They would tell the joke to each other as a  warm up for their acts. While the setup and punchline remain the  same throughout, the middle section, describing the actual family  act, is always varied to get the juices going by throwing in the  most they can and keeping it funny. There are stories of parties  where performers will jam and keep it going for almost an hour.