Kid: Licks money.
Mom: Hey, don’t lick the money. It is dirty.
Kid: Is that why they call people filthy rich?
Kid: Licks money.
Mom: Hey, don’t lick the money. It is dirty.
Kid: Is that why they call people filthy rich?
Hey, listen up, numbskull. The kid licked money, his mom said it was dirty, and the kid made a pun, get it? Filthy rich? The joke is that money is physically dirty, but also associated with people who are "filthy rich."