The sheer physicality of playing a character in chronic pain was the most challenging part of starring in the film “Cake,” Jennifer Aniston said of a leading role that turns one of the world’s most glamorous actresses into a bitter, unpleasant woman. In the film, which had its world premiere at the Toronto International Film Festival on Monday, Aniston plays Claire Simmons, a woman suffering from constant pain and pill addiction who is haunted by hallucinations of a fellow support-group member who committed suicide.
