Nina later has a violent argument with her mother, after which she passes out. Concerned about Nina's erratic behavior, her mother tries to prevent her from performing on opening night; enraged, Nina stands up to her mother and forces her way out of the apartment. Since her mother had called to say Nina was sick, Thomas assigned understudy Lily to take over, but reluctantly gives way when Nina insists on performing. The first act goes well, until Nina is distracted by a hallucination during a lift, causing her partner, playing the Prince, to drop her. Distraught, she returns to her dressing room and finds Lily there. Lily announces she is to play the Black Swan. Nina shoves her into a mirror, shattering it. Lily, seemingly dead, awakens, and her face changes shape, now a copy of Nina's. The doppelganger starts to strangle Nina, who then grabs a shard of glass and stabs her rival in the stomach, apparently killing her. The doppelganger's face reverts to that of Lily's. Nina hides the body and returns to the stage to dance with passion and sensuality.