In Act 4 scene 3, Claudius tries to get Hamlet to reveal where he has hidden Polonius' body. Hamlet tells the King that Polonius is "at supper." Claudius questions, "At supper? Where?"
Hamlet replies irreverently:
Not where he eats, but where he is eaten. A certain convocation of politic worms are e'en at him. Your worm is your only emperor for diet. We fat all creatures else to fat us, and we fat ourselves for maggots. Your fat king and your lean beggar is but variable service- two dishes, but to one table. That's the end.
Here Hamlet is mockingly pointing out that a king and a beggar will both be food for worms. Thus death is the great leveller--both the king and the beggar end up the same in death no matter what their positions have been in life.
Hamlet continues by saying:
A man may fish with the worm that hath eat of a king, and eat of the fish that hath fed of that worm.
Claudius wonders what he means, and Hamlet replies:
Nothing but to show you how a king may go a progress through the guts of a beggar.
Not only has Hamlet pointed out to the King that death will make all the same, but he has given the King the humbling picture of a king's eventual and possible consumption--through a worm and a fish--by a beggar--another image of the work of the great equalizer, death.