When Hamlet and the Ghost were alone, the Ghost spoke. It claimed to be the spirit of Hamlet’s father, murdered by Hamlet’s uncle Claudius. Though the story was that Hamlet’s father was napping in his garden and was stung by a serpent, in reality Claudius poured poison into the his ear, murdering him and sending him to Purgatory because he was not given a chance to confess his sins before he died.
The Ghost commanded Hamlet to avenge him for his murder. The Ghost also warned Hamlet not to harm his mother. The Ghost disappeared at dawn. Hamlet promises to do nothing but seek revenge. He talks badly about his mother Gertrude, “O most pernicious woman!”, then his uncle Claudius. Horatio and Marcellus rush in. Hamlet refuses to tell them what happened, fearing that they’ll reveal it. But he says he will pretend to be insane, and makes them swear to silence on his sword. The Ghost’s voice echoes: Swear! And they swear. Hamlet panics because of the burden the Ghost gave him.