Hamlet is at first not sure whether to believe the ghost, so he tries to investigate. He pretends to be mad to hide what he is doing. As the play goes on, it becomes hard to tell if Hamlet is actually mad or still just pretending. His behaviour causes him to fall out with Ophelia, a girl he was in love with. He eventually has the idea of getting some actors to put on a play of a king being killed in the way the ghost described to see if Claudius reacts guiltily. Claudius panics when he sees the play, and Hamlet sees this as confirmation that he is a murderer.