The bite of a vampire can turn the victim into another vampire; and similarly Verdi's witches exert a field of force that turns others into witches—especially (as we shall see) Lady Macbeth, who has no direct contact with them. Even the witches’ oracular rhetoric is strangely contagious: the great Act I scene and duet for Macbeth and his wife occurs not long after the scene with Macbeth and the witches, and it is remarkable how much both the protagonists start to sound like witches. They start to talk to one another in epigrams.

Just as the witches could hardly keep a straight face as they delivered their prophecies, so the Macbeths’ epigrams retain their serious demeanor with a certain difficulty—they tend to decay into gestures of meaningless fuss. The Macbeths tend to get stuck on a single musical phrase, unable to proceed. For a first look at the operations of a repeated epigram, let us examine the Scena e Marcia (1.2). Macbeth enters—Lady asks him when the king will be leaving, and he replies,Domani, tomorrow; this news inspires her to devise a memorable omen, Mai non ci rechi il sole un tal domani (may the sun never bring us such a tomorrow), her vocal line inching up the first fifth of the C minor scale, then falling back from G to E, with a plagal cadence in the orchestra (E|–A|–E| major—see ex. 23).

The melody of this black prayer will often reappear, in blacker forms: later in this act, when Macbeth addresses a request to the immobil terra, a’ passi miei sta muta! (unmoving earth, be mute to my footsteps!—a harmonic movement from A| minor to E|)—see ex. 24); and at the very beginning of the second act, Macbeth and his wife (whom Verdi and Piave call simply Lady) mull over the consequences of the assassination in a short passage that is simply a tissue of this epigram, repeated over and over. First, Lady tells Macbeth, Why worry?