He is annoyed, but quite willing that Lisa's attractions shall atone therefor. At that moment, however, there is a noise without, and Lisa escapes into an adjoining room. In her haste she drops her handkerchief, which Rodolpho picks up and hangs over the bedpost. A few moments later he is amazed to see Amina, all in white, raise his window and enter his room. He realizes almost immediately that she is walking in her sleep, and that it is her somnambulism which has given rise to the superstition of the village phantom. In her sleep Amina speaks of her approaching marriage, of Elvino's jealousy, of their quarrel and reconciliation. Rodolpho, not wishing to embarrass her by his presence should she suddenly awaken, extinguishes the candles, steps out of the window and closes it lightly after him. Still asleep Amina sinks down upon the bed.
The villagers enter to greet Rodolpho. As the room is darkened, and, to their amusement, they see the figure of a woman on the bed, they are about to withdraw discreetly, when Lisa, who knows what has happened, enters with a light, brings in Elvino, and points out Amina to him. The light, the sounds, awaken her. Her natural confusion at the situation in which she finds herself is mistaken by Elvino for evidence of guilt. He casts her off. The others, save Teresa, share his suspicions. Teresa, in a simple, natural way, takes the handkerchief hanging over the bedpost and places it around Amina's neck, and when the poor, grief-stricken girl swoons, as Elvino turns away from her, her foster-mother catches her in her arms.
In this scene, indeed in this act, the most striking musical number is the duet near the end. It is feelingly composed, and, as befits the situation of a girl mistakenly, yet none the less cruelly, accused by her lover, is almost wholly devoid of vocal embellishment. It begins with Amina's protestations of innocence: "D'un pensiero, e d'un accento" (Not in thought's remotest region).
When Elvino's voice joins hers there is no comfort for her in his words. He is still haunted by dark suspicions.
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An unusual and beautiful effect is the closing of the duet with an expressive phrase for tenor alone: "Questo pianto del mio cor" (With what grief my heart is torn).
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Act III, Scene 1. A shady valley between the village and the castle. The villagers are proceeding to the castle to beg Rodolpho to intercede with Elvino for Amina. Elvino meets Amina. Still enraged at what he considers her perfidy, he snatches from her finger the ring he gave her. Amina still loves him. She expresses her feelings in the air: "Ah! perchè non posso odiarti" (Ah! Why is it I cannot hate him).