Another reason the play is so creepy is that Macbeth and Lady Macbeth themselves increasingly borrow the witches' lexis. Read Lady M's big speech before Duncan arrives, or any soliloquy of Macbeth later in the play. They start speaking in threes, winding up curses, making knowing references to black things like beetles and ravens alongside night and darkness; evil things like horror and poison and venom and "murdering ministers"...and tying them in to ideas like fate—the fatal bellman; fatal visions—and death. Sometimes they refer to their own desires as black and cruel. They essentially become witches themselves.