While the crew was applying blood to the stab wound on Natalie Portman, she commented to director Darren Aronofsky that she was uncomfortable with the placement of the blood on her tights because it looked like a period. Aronofsky told her he intentionally placed the blood where it was to symbolize Nina becoming a woman. As a result, Portman has stated that she doesn’t believe Nina dies at the end of the film. She sees it more as Nina having to kill the little girl in order to mature into a woman.

(Source: filmtrivia)