This scene from 'Joker' was not written in the original script and was improvised by Joaquin Phoenix
In the original script, Arthur Fleck was supposed to show some regret for having killed three people on the Gotham City subway.
After the successful premiere of 'Joker', little by little curious details about Todd Phillips' film are revealed. Screenplayed posted a video where the director reveals that he and Joaquin Phoenix changed a scene at the last minute.
The sequence Phillips referred to is when Arthur Fleck murders three subjects inside the Gotham City subway. After the crime, he comes to a bathroom and starts dancing. This scene is considered by many to be one of the best; however, Todd and screenwriter Scott Silver had thought otherwise.
"In the script, Arthur was supposed to go into the bathroom, hide his gun, wash off his makeup, look in the mirror and ask himself, 'What have I done? '" Philiph commented.
When we got to the set that day, Joaquin and I just stood there and (we felt) this didn't look much like Arthur. Why would Arthur care to hide the gun from him? We released about a million ways to do something different,” he added.
"An hour had passed and I said: 'I got this music from Hildur Guðnadóttir, our composer, and I would like to play this piece of music for Joaquin.' He just started dancing to this music. It was just him and me, alone, in the bathroom. There were 250 people waiting outside. He just started doing that dance and we looked at each other and we knew it was the scene. It made sense to us. When I met Joaquin, I told him that Arthur was one of those people who has music in him. Music and dance became a theme in the film”, he concluded.