metaphor of snake represents threats to Macbeth's power, specifically Banquo and Fleance, as well as guilt and paranoia. To "scotch" the snake means to wound or injure it, suggesting Macbeth's actions have only temporarily removed the threats not eliminated them. Imagery of snake evokes danger, deceit reflecting Macbeth's growing paranoia. By realising snake is still alive, he reveals his realization that his violent acts only led to further danger and unrest. Foreshadows more violence and inability to find peace