The hallucinations that Macbeth experience are used as reminders of his growing evil and desire to be king, as well as the guilt for many deaths. When Macbeth is preparing to kill Duncan, he experiences a vision of a dagger glittering in the midnight air, then suddenly splashed with blood. He calls a ‘fatal vision’ and guesses if it is a ‘dagger of the mind, a false creation, proceeding from the heat-oppressed brain’. The dagger also symbolizes the terrible path that Macbeth is about to begin. The dagger reinforced his plan of action and how the supernatural deceived him into killing Duncan.