Red Kite Eating Carrion
Hamlet says this when he accuses himself of being a coward. He means that if he weren't a coward he would have killed King Claudius and fed his guts to the kites, which are carrion-eating birds.
Hamlet isn't just imagining a fitting punishment for King Claudius. The kind of thing he describes would have been seen by some members of his audience, because a common part of the punishment for treason was for the traitor to be disemboweled while he was still alive, and to see his entrails eaten by dogs and kites.