In act III Scene 2 of William Shakespeare’s play Hamlet, the protagonist Hamlet devises a plan to find out if Claudius is actually guilty of murdering his father, the king of Denmark. Hamlet feels he should not take the story of the ghost for real without finding evidence for it. To do this, he directs a play similar to how the king Hamlet was murdered according to the ghost. He believes that Claudius’ reaction to the play will reveal the truth.
In Hamlet’s play, Gonzago, the Duke of Vienna is murdered by his own nephew Lucianus, who pours poison in his ear while he is sleeping. This scene approximates the alleged murder of King Hamlet by Claudius. Moreover, in the play, Baptista, the wife of the king, agrees to marry the nephew of the king who is the murderer, shortly after the king's death. Hamlet names the play "The Mouse Trap", and comments that the play will not affect anyone who has a clean soul and conscience.
But Claudius gets restless and anxious just after watching this. He stands up in the middle of the play, asks to turn on the lights, and angrily leaves.
KING: Give me some light. Away!
After Claudius says this, Hamlet’s play gets halted abruptly and everyone else, except Hamlet and Horatio, also leaves the place.
Later Guildenstern informs Hamlet that Claudius was exceedingly upset after watching the play.
GUILDENSTERN: Is in his retirement, marvellous distempered.
Claudius’ reaction adds weight to the ghost’s story and makes Hamlet believe that he is, in fact, guilty of murdering the king Hamlet.