Natalie Portman said in an interview with Charlie Rose that one of the most difficult challenges, aside from training and dancing, was her voice in the film. She stated director Mike Nichols gave her consistent criticism on how childish her voice sounded and encouraged her to work with vocal coaches to make it sound deeper and more adult. The role of Nina required Portman to regress backwards to make her voice more child-like. She felt it was taking her back to a point she worked hard to leave behind.