It will have blood; they say, blood will have blood:
Stones have been known to move and trees to speak;
Augurs and understood relations have
By magot-pies and choughs and rooks brought forth
The secret’st man of blood.

– William Shakespeare

Macbeth, Act 3, Scene 4. Macbeth recalls an old saying about the murdered dead having their revenge. Haunted by guilt, he fears that his shedding of Banquo’s blood will lead to his own death. His murder of his friend may be discovered by supernatural means, he believes. Macbeth is aware that stones have moved, trees have spoken, birds have told secrets. All of these things have identified murderers like Macbeth – “the secret’st man of blood.” This is foreshadowing of Macbeth’s own violent death.