I think the most interesting part of Cake is the amazing performance of Jennifer Aniston as Claire Simmons. She is a well-off L.A. divorcee who is a chronic pain sufferer due to the fact she was in a car accident that killed her son and left her with physical and emotional scars.
Claire is cranky, bitter, lies, steals to get what she wants, usually Percocet and the like. Even the people who are paid to be nice to her can’t stand her. She gets kicked out of her support group for expressing her admiration for a member who had leaped off the freeway overpass to her death.
Thank goodness the relationship between Claire and her Mexican housekeeper provide her saving grace. Claire still is rude to Silvana but comes to her rescue in one scene which gives the viewer a hint that there is some kindness under that horrible behavior.
As the movie progresses you wonder: will she ever clean up her act or have the ultimate meltdown?