When Cash wakes up on the tour bus, just after the Folsom Prison performance, he walks past guitarist Luther Perkins, who is passed-out with a lit cigarette in his mouth, and puts the cigarette out. Perkins died a few months after the 'At Folsom Prison' recording/performance. He fell asleep in his Tennessee home with a lit cigarette in his mouth, and died from injuries sustained in the resulting fire.
During one scene Johnny Cash is high and performing "I Got Stripes", he walks right up to June Carter and glares at her for an uncomfortably long period of time on stage. According to the director, James Mangold, this was unscripted and improvised by the actors. Mangold said that he simply told Joaquin Phoenix to do what he would do in real life if he were angry at his girlfriend and then had to perform on stage with her. Much to Phoenix's surprise, this backfired and Reese Witherspoon responded to his actions by simply rolling her eyes, and continuing to perform the song. Phoenix later said that her reaction threw him off because his goal had been to make her as uncomfortable as possible on stage.
The director said that Joaquin Phoenix and Reese Witherspoon developed a very codependent relationship during filming. According to him, after the filming wrapped, Phoenix admitted to him that he and Witherspoon had relied on each other so much that they made a secret pact. The deal was that if one of them left or dropped out, the other would leave as well.
Reese Witherspoon and Joaquin Phoenix were both so nervous about having to sing that it caused tension in their relationship off screen. Both actors admitted in interviews that they didn't get along and constantly argued during the six months of singing lessons prior to filming. It wasn't until filming started that they connected and became friends.
According to director James Mangold, when Joaquin Phoenix was learning how to sing and play guitar like Johnny Cash, his voice was too high and the band learned how to play Cash's songs in a higher key. Just before filming started, Joaquin's voice dropped closer to John's level, and the band had to re-learn the songs in their original key.
In the 1956 Sun Records recording of "I Walk the Line," Johnny Cash flubs the final low note ("because you're MINE"). Joaquin Phoenix flubs the same note, in the same manner, in the film, as he sings "I Walk the Line."
When Johnny Cash first approaches the recording studio, a pair of young men are rhythmically polishing shoes; an homage to Johnny Cash's song "Get Rhythm," in which he sings about a shoeshine boy on the corner of the street.
Johnny gets fan mail from a Folsom Prison inmate named Glen Sherley. In real life, Sherley was an inmate at Folsom when Johnny Cash recorded "At Folsom Prison." He also wrote "Greystone Chapel," which Johnny recorded during the show.
Towards the end of the movie Johnny tells his Dad to tell the girls about the flood. This is a reference to a real incident in Johnny Cash's childhood when the family farm flooded that he wrote and sang about in his famous song 'Five Feet High and Rising'.
When James Mangold asked Johnny Cash what his favorite film was, the singer replied Frankenstein (1931) - "because it's about a man made up of all these bad parts and yet he still tries to do something decent and be someone decent".
After visiting many of Johnny Cash's old homes, production designer David J. Bomba created 90 different sets for the film and tried to underline the contrast between Cash's two lives, one that was close to earth and nature in Arkansas and Tennessee, and the other set in the fast-moving world of rock music.
Kathy Cash, Johnny's second oldest daughter with his first wife, Vivian, walked out of a family screening of the film five times. She felt Phoenix and Witherspoon performances were "Oscar-worthy", but that her mother, Vivian, was cast in an unfair light. Also, she did not feel there were enough scenes of Johnny interacting with his children, and that the film portrayed his father too harshly. When her half-brother, John Carter Cash (an executive producer of the film) was asked about her reaction, he responded that the movie was intended to tell the love story between his mother and father.
The screenplay was sent to Joaquin Phoenix on a Friday. He called James Mangold on Monday morning, asking what he needed to do to play the part of Johnny Cash. Mangold told him to go out and buy a guitar, which Phoenix duly did the next day.
For the Folsom Prison sequence, Joaquin Phoenix insisted that the crew members playing the wardens didn't let the extras playing inmates eat, drink or go to the toilet. This helped create a particularly tense atmosphere on set.
There was a consensus opinion that the only reason Walk the Line (2005) got greenlit was because of the success of Ray (2004). The truth is that this film was well into production when Ray (2004) first came out.
The film owes its genesis to a 1993 episode of Dr. Quinn, Medicine Woman (1993). Johnny Cash was guest starring on the show and had become friends with the star, Jane Seymour, and her husband, director James Keach. Cash suggested to Keach that he should tackle a film of the singer's life which he readily agreed to, so Keach and Seymour started compiling interviews with Cash in preparation for a script. By 1997, Gill Dennis had enough material to put a screenplay together but the project had stalled. That's when Keach reached out to James Mangold, knowing the director had been lobbying hard for the chance to get involved.
Reese Witherspoon grew up in Nashville, Tennessee and was a huge fan of Dolly Parton growing up. In her Oscar acceptance speech, she thanks the film's music director/producer T. Bone Burnett for "helping me realize my childhood dream of being a country music singer."
The trivia item below may give away important plot points.
Johnny Cash really did propose to June Carter Cash onstage. It happened in February 1968, at the London Ice House, a hockey arena in London, Ontario, in the middle of a performance of "Jackson". She accepted, and they married a week later.