Hamlet (Act 4, scene 3)
So Claudius is demanding to know where Polonius is. Spoiler alert: Hamlet murdered him. He jokes that Polonius is currently being eaten by worms. He also says:
A man may fish with the worm that hath eat of a king, and eat of the fish that hath fed of that worm.
What dost you mean by this?
Nothing but to show you how a king may go a progress through the guts of a beggar.
Basically: a worm eats a dead king. A man uses the worm to fish, then eats the fish that ate the worm. Saying a king like Claudius may “progress through the guts of a beggar” is just Hamlet’s really elaborate way of calling his uncle a turd. Good one, Hamlet. You really got him.