This is the Joker’s diary. In order to inhabit his character, he locked himself up in a hotel room for weeks. He would do that. He liked to dive into his characters, but this time he really took it up a notch.
The hospital scene is interesting because when he was a kid, his sister Kate liked to dress him up as a nurse. He was really funny like that. He also was in the movie. This is a make-up test which was done eight months before. Before the end of the shooting he wrote ‘bye bye’ on the back of the page. It was hard to see this.