"For the first time in probably 25 years I watched dailies. So [director Todd Phillips] and I would talk about which takes we thought worked. But my favorite scene, what both of us thought was my best scene because of a particular take, that scene is not in the movie," Phoenix, 44, told The Associated Press.
"It's a cliche, but it's a puzzle. So you take out this scene and it affects the following scene. So a take that might have been really great no longer works. The best take for the end of his rant on Murray Franklin [Robert De Niro's talk show host character] just didn't work. It was a really good take just on its own but cut in with everything else it just didn't work. An earlier take, one that I didn't think was very good, was the one that worked best."
Phoenix said he and Phillips did a slew of experimenting with different takes and interpretations of the notorious Batman villain's actions, which he thinks made him a stronger actor overall.
"There seemed to be an infinite number of ways to interpret every moment or how he might behave in any moment. And there wasn't anything that didn't make sense," he explained. "So we would do scenes so many different ways and some I would cry and others I would make jokes and others I would be angry and it would be the same scene and they all f—king made sense and that's so rare. There's something really exciting about that because it keeps you in this state of like perpetual investigation and trying to find something new."
"I think Todd and I were always working to try to surprise each other with some idea," he added. "There was never a moment that I felt completely relaxed. I was always searching for something else. And there's something very exciting about that. It's so much fun acting in that way. Often times it's the opposite."
Phillips, meanwhile, is irked by critics of the film from the far left who slammed the movie before they even got a chance to see it.
"It's a little troubling when people write think pieces without having seen it. And even in their think pieces write, 'I don't need to see it to know what it is.' I find it astounding, to be quite frank, how easily the far left can sound like the far right when it suits their agenda," Phillips said. "To that point, I've been disappointed."
The preemptive backlash is all the more baffling to Phillips because he hopes "Joker" inspires conversations: About guns, about violence and about the treatment of people with mental illness.
"Part of the reason we made the movie is a response to the comic book world of movies," Phillips said. "Like, 'Why is this celebrated? Why is this funny? Why is this fun? What are the real-world implications of violence?'"
The film itself is a slow-burn character study of how a mentally ill, middle-aged man named Arthur Fleck becomes the Joker. When the audience drops, he's working as a clown-for-hire, living with his mother in a run-down Gotham apartment and checking in occasionally with a social worker. He has a card that he gives to people to explain that his spontaneous and painful bursts of laughter are because of a medical condition. His only joy seems to be watching the talk show host Murray Franklin (played by Robert De Niro) in the evenings.
"The truth is you see it and it's heartbreaking. And he's heartbreaking," Phillips said. "And you know what happens in the movies when you have a world that lacks empathy and lacks love? You get the villain you deserve."
It's a role that has often required actors to go to difficult places, and this "Joker" has the added complication of being more realistic than most of the other depictions even though it's still set in a fictional world. To play Arthur and Joker, Phoenix researched a number of people that he's reluctant to even name.
"Some of the people I studied, I feel what they crave is attention and notoriety," he said. "I don't feel like they deserve any more of that."
The Associated Press contributed to this report.