1. To accomplish the Joker character, actor Joaquin Phoenix followed an extreme diet and lost nearly 24 pounds.

2. Arthur Fleck himself was conceived with Phoenix in mind.

3. As he prepared for the role, Phoenix studied the movements and mimics of silent film actors such as Buster Keaton and Ray Bolger.

4. Arthur's clown makeup was made to look "antique" - the lips were dyed red to resemble blood.

5. Part of the script changed the day before the filming and the actors had to adapt - which made it better - and in some cases improvise.

6. During the filming, Hildur Guðnadóttir (Icelandic musician, who was entrusted with film music) was placed in the background, so that the actors could be more involved.

7. Guðnadóttir's music changed a scene. In the scenario, it was envisaged that Arthur would run to the bathroom, wipe the gun and wash his face. Hearing the music in the background, Phoenix began to dance. Producer Todd Philips decided not to cut it as a stage.

8. Joaquin Phoenix had a clash with his favorite American actor, Roberd De Niro. De Niro wanted to take a look at the script before filming, while Phoenix insisted on not reading it.

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