I know this joke! (or something similar - I have heard variatiions)
It's to do with a tribal leader, and he has 2 sons with 2 of his wives (his squaws). His third wife gives birth, and he holds a competition to guess about the birth of his third wife. Many come, and guess girl, boy, etc. At last, one of the tribe guesses twin boys. The leader is amazed, and asks how he did this.
Anyway, the punchline is the pythagorean rule. I'm pretty sure the version I remember had a 'high-pot and noose'. Hmm