After MacBeth has killed King Duncan, he looks at the blood on his hand and wonders if he will ever be free of the stains of guilt. (Will all great Neptune’s ocean wash this blood/Clean from my hand? II ii 61). Blood becomes a repeated image, also symbolizing the guilt of killing and betraying.
His blade stung against her neck, digging into the flesh ever so slightly. "Arrogant boy," she glared. "Have you already forgotten that what we do may not hurt now, but when the new cycle comes we will feel his perdition?"