Macbeth’s trepidation about the murder is echoed by several portentous sounds and visions, the famous hallucinatory dagger being the most striking. The dagger is the first in a series of guilt-inspired hallucinations that Macbeth and his wife experience. The murder is also marked by the ringing of the bell and the knocking at the gate, both of which have fascinated audiences. The knocking occurs four times with a sort of ritualistic regularity. It conveys the heavy sense of the inevitable, as if the gates must eventually open to admit doom. The knocking seems particularly ironic after we realize that Macduff, who kills Macbeth at the end of the play, is its source. Macbeth’s eventual death does indeed stand embodied at the gate.
The motif of blood, established in the accounts of Macbeth’s and Banquo’s battlefield exploits, recurs here in Macbeth’s anguished sense that there is blood on his hands that cannot be washed clean. For now, Lady Macbeth remains the voice of calculating reason, as she tells him that the blood can be washed away with a little water. But, as Lady Macbeth eventually realizes, the guilt that the blood symbolizes needs more than water to be cleansed away. Her hallucinations later in the play, in which she washes her hands obsessively, lend irony to her insistence here that “[a] little water clears us of this deed” (2.2.65).