Final answer:
In the play 'Macbeth', Macbeth hallucinates a dagger before killing the King. The dagger represents his ambition and foreshadows the violent act.
Step-by-step explanation:
In the play Macbeth by William Shakespeare, before killing the King, Macbeth thought he saw a dagger in the air in front of him. This hallucination is known as the 'dagger soliloquy' and it represents Macbeth's internal struggle and the influence of his ambition. The dagger symbolizes Macbeth's desire for power and foreshadows the violent act he is about to commit.