Hamlet Act IV, Scene iii Summary

Claudius demands that Hamlet tell him where Polonius's corpse is.
Hamlet responds with morbid jokes, pointing out that Polonius is at "supper" – that is, he's being eaten by worms for dinner. Hamlet, again speaking in the veiled terms of seeming madness, describes the cycle of life, where a worm can eat a king, a fish can eat that worm, and a man can eat that fish, thus eating a king, who, inevitably passes through the digestive system of another man. Basically, Hamlet calls Claudius a piece of poo.
This is obviously a threat to Claudius.
Claudius presses on about Polonius's lost body, and Hamlet admits the whole "find the body" game will be a lot simpler once Polonius's corpse begins to leave a reeking scent trail.
After Hamlet hints that the body is in the stairs leading to the lobby, Claudius sends the attendants off to find the body.
Claudius tells Hamlet he's being shipped off to England with Rosencrantz and Guildenstern for his own good, and also as a princely time-out for having caused so much trouble.
Claudius, left alone, reveals that he has arranged to have Hamlet killed once he reaches England.