What does Hamlet mean when he say this to Claudius in act 4 scene 3?"A man may fish with the worm that hath eat of aking, and eat of the fish that hath fed of that worm. "
Hamlet is always taking digs at his Uncle Claudius--in clever ways. Hamlet is insulting his Uncle here, by saying that someone could go fishing, and bait his hook with a worm that could have been feeding on a dead body in the earth. (And not just any body, but the body of a king!)
If the fisherman caught a fish with that particular worm, he'd be eating both the fish and the worm--because we all get nutrients from what we eat, right? And since the worm ate from the flesh of the dead body, the fisherman could, in essence, be eating the king.
This is Hamlet's roundabout way of telling Claudius that we are all the same, especially in death. Our rank or class doesn't matter--we are all vulnerable, anyone can attack or harm us, etc.