Todd Phillips said in an interview with the New York Times that Joaquin Phoenix sometimes lost his composure on set, and even walked off in the middle of some scenes. According to Phillips, Phoenix would suddenly get up and walk out in the middle of a scene, and the other actor would take it personally, even though the problem was never with them but with Phoenix not feeling the moment. Phoenix would leave the set for a while to breathe, but he always came back. Phillips recounted that after a particularly tense moment, Phoenix reassured him by saying, "We'll take a walk and come back and do it." The only person Phoenix never abandoned was Robert De Niro. In a statement to The Times, De Niro said Phoenix was "a perfect professional" on set: "Joaquin was very intense in what he was doing, as it should be. There's nothing to talk about personally, like 'Let's have coffee.' Let's just do our work."
The film mentions that giant rats are seen in Gotham. If you pay attention, you can see at least three CGI giant rats running quickly through the streets in key scenes, adding a disturbing element to the film's already dark atmosphere: the scene where Arthur talks in the phone booth (around the 29th minute), the scene where Arthur chases the last yuppie in the subway (around the 34th minute), and the scene where Bruce cries over his parents' bodies (around 1 hour 50 minutes).
The scene where Arthur rips the card-printing machine off the wall and throws it was not in the script. In an interview, Leigh Gill (Gary) said that during a take, Joaquin Phoenix suddenly decided to make a joke about making an exit and ripped the machine off the wall and threw it.
Asked a question about the violence in the R-rated film, Todd Phillips gave this answer: "The violence in the film was always designed as a slow burn. People think it's going to be a very violent film; but it affects you differently. You can watch something like John Wick 3 and there's a much higher amount of violence. We tried to paint the violence with as realistic a brush as possible so that when it comes, it feels like a punch to the gut. But it's all a tonal balance." On the question of tone, he added, "I think films are often mirrors of society, never the shapers of it. We wrote this in 2017, so inevitably some themes find themselves." When he continued with "This is not a political film," laughter rose in the press room, and he added, "For some, I think it depends on which lens you're looking through."
As a result of a conscious effort to keep the budget low, there are almost no CGI-effect shots in the film. One of them is the scene where Arthur Fleck walks toward Arkham State Hospital to look at his mother's medical records. This scene was enhanced with CGI, but most of the film's effects were either practical or created in camera.
In the first take of the scene where his character looks in the mirror, Joaquin Phoenix unexpectedly shed a tear, and director Todd Phillips used it. Phillips said he played the film's music for Joaquin Phoenix because he "wanted the music to affect and infect the set." While the music played during the first take, Phillips explained, "Joaquin, this little tear appeared as Arthur was struggling with his smile, and we took the scene and moved on."
In August 2018, Hildur Guðnadóttir was hired to compose the film's music. Guðnadóttir began writing music after reading the script and met with Todd Phillips; Phillips had "very strong ideas" about how the music should be. She worked on the Joker score simultaneously with the music for the drama miniseries Chernobyl (2019); Guðnadóttir said that switching between the two was difficult because the two scores were so different. She won a Grammy, an Emmy and an Oscar for both works.
Writer-director Todd Phillips, inspired by Sergio Leone, unusually asked composer Hildur Guðnadóttir to write the music before the film was shot. The aim was to use the music to set the mood on set while shooting the scenes.
Joaquin Phoenix improvised the scene where Arthur gets into the refrigerator.
In the scene where Arthur is among the audience at a comedy club, the comedian performing is stand-up comedian Gary Gulman. His performance about role-playing with his girlfriend can be heard on Gulman's 2012 album "No Can Defend."
Joaquin Phoenix improvised the bathroom dance scene on the spot. In the script, Arthur simply runs into the bathroom, hides the gun, washes his face and talks to himself while looking in the mirror.
The argument between Arthur and Thomas Wayne in the bathroom was improvised by Joaquin Phoenix and Brett Cullen.
According to director Todd Phillips, a certain scene had to be cut so the film would not receive an NC-17 rating. This scene is the one where Arthur is in the bathtub. Phillips describes the scene as "unbelievable" but chose not to leave it in the theatrical cut, fearing the MPAA's reaction could cause the film to lose its intended R rating. The scene was one of many that were shot but ultimately removed from the theatrical cut. Phillips said, "I don't think we could put that in an R-rated film, and it's not because it was pornographic, it was just crazy." This created great curiosity about the scene.
In the German, Italian, French, Spanish, Russian and Hungarian versions of the film, Arthur's journal entries and the card explaining his condition are in the respective national languages. This is quite unusual for a live-action film because it required producing extra props and then shooting them.
Todd Phillips said of the iconic stairs: "We thought it would be a pretty iconic moment for the film, I didn't know the stairs would become something like New York's Rocky steps," he laughed.
The only scene in which Arthur Fleck does not appear is the scene near the end of the film in which Thomas and Martha Wayne are shot and killed by one of the protesters during the riot.
Editor Jeff Groth, in an interview with The Cutaway, said the following about the cuts in the dark moments on the train: "Not every cut happens on a flash. The reason those flashes are there was to disorient the audience and turn that whole sequence into a kind of fever dream for Arthur." Groth later said: "Most of the time, with a cut, you predict what you want to see in the next step and we take you there. In a case like that, when you cut inside the black, you expect to see the same thing when you come out of the black. But in our version, when you cut [inside the black], you see something different. So we jump perspectives before you as an audience member are ready for it. The aim of that was to create anxiety and build tension." Groth later talked about how this scene gives the audience the feeling that they have lost control: "When [Arthur] starts that laugh, it's something he can't control. Another thing we were trying to evoke is the feeling that we no longer have control." The film constantly moves back and forth between Arthur's fantasy and Arthur's reality, and the audience doesn't know it. The feeling that we don't have control points to the fact that Arthur is the unreliable narrator of his own story and that the audience never knows what is really happening.
The application of Joaquin Phoenix's Joker makeup took 15 to 20 minutes. In a discarded version of the scene in which Arthur does his bathroom dance, he was washing off his makeup before leaving. About 16 takes of the scene were shot, and makeup artist Nicki Ledermann had to reapply the makeup each time to maintain consistency.
On September 22, 2018, a violent protest scene was shot in Brooklyn, but the station was altered to look like Bedford Park Boulevard. In late September 2018, the robbery scenes were shot at the First Central Savings Bank in Astoria, Queens. According to Zazie Beetz, Todd Phillips rewrote the entire script during production because Joaquin Phoenix had lost so much weight for the film and there would be no chance to reshoot. She recalled: "Todd would go to his trailer and write the scene for the night and then we'd do it. During hair and makeup I'd memorize those lines and then we'd do it and three weeks later we'd be reshooting it."
Film composer Hildur Guðnadóttir performed the cello solo sections herself.
Sharp-eyed residents of New York will immediately recognize the Brooklyn Army Terminal annex as Arkham State Hospital. For Arthur Fleck, this hospital is a constant turning point, as is evident in his conversation with the social worker at the beginning of the film. His mother's records show that both members of the Fleck family went in and out of this grim state facility.
Todd Phillips initially wanted to shoot the film with 70 mm film cameras, but abandoned the idea due to the tight budget. The abundance of close-ups and his desire to give the film an intimate, unsettling atmosphere also led him to rule out standard RED digital and 35 mm film cameras. Cinematographer Lawrence Sher looked into Arri Alexa 65 digital cameras as a compromise, and ultimately these cameras were used.
A month after the film's release, right after it passed 1 billion dollars worldwide, a short video of Joaquin Phoenix dancing on the stairs in his Joker costume went viral. Shot by an unknown person living in the Bronx, this video documented the film's iconic scene.
Costume designer Mark Bridges designed Arthur Fleck's wardrobe from polyester and with the color palette of the early 1980s. "I imagined that if he did laundry, everything would go into the machine at the same time. We gave the clothes a bad-laundry feel," said Bridges, noting that these subtle choices tell the audience who the character is and how he lives.
When production moved to New Jersey, filming began in Jersey City on September 30 and closed Newark Avenue; filming in November closed Kennedy Boulevard. Filming in Newark continued between October 13 and 16. During this time, SAG-AFTRA received a complaint that extras in Brooklyn were locked in subway cars for more than three hours, but the issue was resolved when a representative visited the set. In October, Dante Pereira-Olson and Douglas Hodge joined the cast. Whigham said that at the end of October the production was "midway" through and that it was an "intense" and "incredible" experience. In mid-November filming returned to New York and was completed on December 3, 2018; Todd Phillips marked the occasion with a photo on Instagram.
The song chosen for Joker's dance on the stairs was "Rock 'N Roll Part 2" from Gary Glitter's 1972 album "Glitter." The revelation in the late '90s that Glitter was a sex offender and his prison sentences for child sexual abuse made the use of the song controversial.
Several versions of Arthur's appearance on the Murray Franklin Show were shot. In one version that appeared in the trailer, there was a short shot in which Arthur was already dancing when the curtains opened.
The circular tattoo on Joaquin Phoenix's left bicep was digitally removed in the scenes in which Arthur is shirtless.
In the climactic Murray Franklin Show sequence, two moments highlighting producer Gene Ufland, played by Marc Maron, were shot but cut in post-production. In the first, Gene openly expresses his concerns to Murray about Arthur being on the show. In the second, Gene tries to cut off the interview in which Arthur confesses to the subway murders, but Murray ignores him and turns off his microphone. Gene then watches in silent horror as Murray is killed.
The staircase that Arthur Fleck repeatedly climbs and descends is now known locally as the Joker Stairs. Located in Highbridge in the Bronx, New York, this stepped street connecting Shakespeare and Anderson avenues at West 167th Street has become one of the film's iconic locations.
At around the 35th minute, the scene in which Arthur dances in a public restroom inspired funny videos on TikTok in which people dance in a similar way when something bad happens to them. Composer Hildur Guðnadóttir's music was also used in these videos.
The film contains a total of 162 visual effects.
In the official trailer, at 1:35, there is the moment when Arthur falls on the entrance steps of Wayne Hall and Modern Times (1936) is being screened; at 2:03, there is the scene in which Arthur, in his Joker costume, walks down the corridor of his building with flowers in his left hand. Both scenes were cut from the film.
The same stepped street known as the Joker Stairs had previously been used in A Walk Among the Tombstones (2014), starring Liam Neeson.
The location used for Wayne Manor is the same as in Batman Forever (1995): Webb Institute of Naval Architecture - Stevenson Taylor Hall, The Braes, Glen Cove, Long Island, New York.
Despite its R rating, the film uses the F-word only 27 times.
Some released stills show a scene in which Arthur meets Randall on the street in his clown costume. This scene was also cut from the film.
The film's logo was created by graphic designer Chad Danieley. Danieley prepared the logo with a wooden letterpress machine and then digitized it.
After the film's release, the staircase where Joaquin Phoenix performs his iconic dance became a popular tourist attraction. Many visitors recreated the scene in Joker costumes, but after complaints from Bronx residents who use the stairs for daily transportation, New York's 114th District representative Alexandria Ocasio-Cortez warned visitors not to recreate the dance, because it was causing overcrowding due to crowds taking photos and using selfie sticks.