This scene, like Scene 3, starts with a bold imperative: "Hang out our banners on the outward walls." Macbeth's speech is warlike and defiant, his strength mirrored in that of the castle and men who surround him; his curse on the enemy vivid and graphic in its use of metaphor: "Here let them lie / Till famine and the ague (disease) eat them up . . . " (3–5). But the curse is empty rhetoric: In his play Troilus and Cressida, written two or three years earlier, Shakespeare had written that man's ambitious appetite for power, once it has preyed on everything in its path, can eat up only itself. Power-seeking tyrants tend toward self-destruction; if this curse falls on anyone, it's likely to be the curser.
At this point, Macbeth hears a heart-stopping scream. While a servant is dispatched to find the cause, Macbeth confesses in a brief soliloquy that such noises no longer have the power to frighten him. The audience recalls other noises: the owl-shriek that Lady Macbeth heard during Duncan's murder; the voice that Macbeth heard crying "Macbeth shall sleep no more!" and the fateful knocking at the door, all in Act II, Scene 2. But in a phrase that calls to mind the banquet scene (Act III, Scene 4), Macbeth admits that he has "supp'd full with horrors" and that his familiarity with slaughter means that such sounds can no longer amaze him.
