Due to a dislocated rib injury, Natalie Portman had to receive physical therapy during filming. Portman is undergoing a real therapy session in one scene with Michelle Rodriguez, an actual physical therapist brought in by choreographer Benjamin Millepied. Director Darren Aronofsky told Portman to stay in character during the appointment so he could film and include the scene into the final cut.

(Source: filmtrivia)