Through the images, we learn that Minnie's life as John's wife was not a pleasant one. It kept her from being part of the world outside the home. He was like a caged bird dying to be freed. Which leads to another part of the play, Mrs. Hale finds a caged bird, which has been strangled to death. Minnie did this to show how she felt. Locked up and dying to be released, but John has strangled her life and made her escape impossible. This explains how John controlled Minnie, she couldn't stand the feeling of being trapped