Sal at one point berates one of the bank tellers for smoking, saying he doesn't smoke because "I don't want to get the cancer". John Cazale was a heavy smoker who died from lung cancer three years later.
The entire film is mostly improvised, though around the script. After rehearsing the script for weeks with his cast, Sidney Lumet took the improvisations that were made while rehearsing and made that the official screenplay.
Another notable improvisation in the film was John Cazale's answer to Al Pacino's question of where in the world he'd like to fly to. Pacino's surprised response was absolutely genuine as he had no idea what Cazale was going to say.
Although he had initially agreed to play the part of Sonny, Al Pacino told Sidney Lumet near the start of production that he couldn't play it. Pacino had just completed production on The Godfather: Part II (1974) and was physically exhausted and depressed after the shoot. With his reliance on the Method, Pacino didn't relish the thought of working himself up to a state of near hysteria every day. Lumet unhappily accepted the actor's decision and dispatched the script to Dustin Hoffman. Pacino changed his mind when he heard that his rival was in the fray.
John Cazale was cast at Al Pacino's insistence, despite being nowhere the age of the real Sal, who was 18 at the time. Sidney Lumet was opposed to the idea because the actor was clearly inappropriate for the part. However, when Cazale came in to read for the part, Lumet was sold on him within 5 minutes.
During production, Al Pacino reportedly only slept a couple hours a night, ate sparingly, and would sometimes take cold showers; this was in order to emphasize Sonny's disheveled, exhausted and yet wired appearance.
Penelope Allen, who plays the blonde chief bank teller, was a surrogate mother to Al Pacino. When he first left home in his teens to pursue acting, he lived with Allen and her husband for several years.
The bank's manager Robert Barrett later said he had more laughs in that one night than he'd had in weeks, while teller Shirley Bell said if they'd been her houseguests on a Saturday night it would have been hilarious.
In the 1972 "Life" magazine article that inspired the film, P.F. Kluge and Thomas Moore describe robber John Wojtowicz as "a dark, thin fellow with the broken-faced good looks of an Al Pacino or a Dustin Hoffman". Al Pacino, of course, played the role based on Wojtowicz, and when he nearly quit the film early on, the role was offered to Dustin Hoffman.
Halfway through the production, Al Pacino collapsed from exhaustion and had to be hospitalized for a short time. After production was completed, he decided to stop doing films for a while and return to stage work.
Because of the outrageous quality of the real life story, Sidney Lumet deliberately chose not to look at any of the footage of what actually happened that day. For that same reason, he decided not to use any of the real Sonny and Leon's wedding film footage as it was so over the top, it would have alienated viewers.
The original working title was "Boys in the Bank." Director Sidney Lumet hated it because he thought it made the film appear to be a "light, fluffy comedy," and he had it changed to "Dog Day Afternoon." He wanted a title that suggested a hot, stuffy day near the end of the summer.
Sidney Lumet made Al Pacino do the phone conversation with Leon a second time even though his first take was perfect. Lumet's reasoning was because he saw how much the scene took out of his actor and he wanted Pacino to look exhausted, as the character had been holed up in a bank, and a highly stressful situation, all day.
Al Pacino first heard about the incident upon which the film is based when it was actually taking place. He was later bemused by reports after the event that the lead participant would make a great role for him.
Al Pacino waves a handkerchief to signal the police when he comes out of the bank. However, John Wojtowicz, the man the movie is based on said that he never waved a handkerchief because he said that he felt that that was a form of surrender.
Right after Sal fires his gun because they think the cops are sneaking in through the back of the bank, Sonny comes outside and gets yelled at by Sergeant Moretti. For this scene, Sidney Lumet told Charles Durning to improvise, and to immediately get Sonny on the defensive. He had three cameras rolling to capture whatever happened; watching the scene, you can feel the spontaneous energy and confusion from both actors. It was an effective use of improvisation (though Lumet said he never tried it again).
Sidney Lumet's team hired about 300 extras to play the crowd that gathers outside the bank during the standoff. According to Lumet, the crowd would swell every day they filmed, especially in the late afternoons, and that the professional extras did a great job of getting the civilians to act appropriately for the scene. It was like a big improv exercise. People who lived on the block were offered hotel rooms if they wanted to get away from the commotion, but most chose to stay. They were invited to look out their windows and gawk, just like real neighbors would do.
After the initial title sequence (Elton John, "Amoreena") there is no background or incidental music on the soundtrack (the start of the Looney Tunes opening music is heard after the TV/phone interview, but it's cut-off after a few seconds, and also Uriah Heep's "Easy Living" is heard briefly through a hand-held radio.).
Early in the writing proceedings, Frank Pierson considered dropping out of the project but had to continue because he had already spent his advance. Struggling to find a hook, he discovered while researching the story of Sonny Wojtowicz, that everyone who knew him had a contradictory story about the man. One thing they all agreed on was that Sonny was always saying "I'll take care of you. I'll make you happy." Pierson then knew that he had found his way in to the story.
The bank where the robbery took place was a branch of the Chase Manhattan Bank, at 450 Avenue P on the corner of East 3rd Street, in Gravesend, Brooklyn. It is today the home of the Brooklyn Medical Imaging Center.
Frank Pierson was unable to pick up his Academy Award for Best Original Screenplay because he was filming A Star Is Born (1976) at the time. Cast and crew stopped filming briefly to go for a quick drink at a nearby bar and then it was straight back to work. Interestingly, this same film is featured on a theater marquee during the opening scenes of Dog Day Afternoon (1975)
For the lengthy phone conversation between Sonny and Leon - largely improvised by Al Pacino and Chris Sarandon - Sidney Lumet was faced with the problem of what to do when the film in the camera ran out as it was only good for 10 minutes worth of film. He solved that problem by starting a second camera up just as the first was due to finish.
Elton John's Amoreena was placed at the beginning of the movie by editor Dede Allen because the opening scenes were shot without sound. The song was also placed at the beginning so that it would give a certain flow to the opening footage while editing it together. After that sequence was cut together, the song was taken out and then the rights were acquired to put it back in because Sidney Lumet missed it.
Most of the movie takes place in three locations: inside the bank, on the street outside the bank, and in the barbershop across from the bank. Standard procedure would be to shoot the street scenes on location, and then film the bank and barbershop interiors on sets constructed at a studio (where it's much easier to control lighting, sound, etc.). But Sidney Lumet wanted realistic continuity. He wanted us to see, for example, that when a character enters the bank from the street, he's really doing that-not walking through a door and emerging on a fake set miles away. Lumet got his wish and found a block of a Brooklyn street that suited his purposes, including a vacant warehouse that could be turned into a bank.
Frank Pierson wrote the screenplay. At one point Al Pacino's character says to one of the bank tellers, "Get your mind right." The same line was constantly used throughout Cool Hand Luke (1967), a movie also written by Pierson.
In the early stages of the robbery, a phone rings in the bank and Sonny Wortzik picks it up, sarcastically says, "WNEW plays all the hits," and hangs up the phone. WNEW, at the time, was a progressive rock radio station not known for playing the Top 40 hits of the day. It is now WWFS, a "hot adult contemporary" station that features performers such as Katy Perry, Madonna and Britney Spears.
Sonny's (Al Pacino) cry of "Attica, Attica!" to stir up the crowd was improvised. Charles Durning's confused reaction was completely natural, as he wasn't sure what his character was supposed to do next.
As a testament to the authenticity of the Foley effects, when Sal racks the M-1 carbine you can hear the twisting of the bolt as it enters the self-cleaning phase of loading. It is a unique aspect to the weapon, as most automatic or semi-automatics do not use a rotating bolt, some exceptions being the M1 Garand, M-1 carbine, and M-14.
The trivia items below may give away important plot points.
Based on the real-life story of John Wojtowicz. On 22 August 1972 he and Salvatore Naturale attempted to rob a branch of the Chase Manhattan Bank on the corner of East Third Street and Avenue P in Brooklyn. They held nine bank employees hostage for over 14 hours. Wojtowicz was trying to get money for his lover, Ernest Aron, to have a sex change operation. Naturale was killed in the standoff and Wojtowicz received 20 years in a federal penitentiary. Wojtowicz was paid $7,500 plus one percent of the net movie profits for the movie rights for his story. He gave $2,500 to Aron to have the operation. Aron had the surgery and changed her name to Liz Eden. She died of AIDS in 1987. Wojtowicz was released from prison after serving 5 years of his 20-year sentence. He died of cancer in 2006.
In the original script, Sonny and his trans-sexual lover were supposed to take part in a scene outside the bank in which a heart-felt goodbye was to take place along with a kiss. Al Pacino refused to do this, claiming it would take away from the phone conversation between Sonny and Leon. Frank Pierson was forced to make appropriate changes. This resulted in just the telephone conversation instead.
Al Pacino originally grew a mustache as a way to help him deal with the fact that he was playing a gay man. In Sidney Lumet's words, however, Pacino's mustache "looked terrible." And after the first day of filming, Pacino agreed. Watching the footage, Pacino told Lumet, "The mustache has got to go," and asked if he could shave it and redo that day's work. Lumet agreed, and the mustache was gone-as was a day's worth of footage.
Even though this film is about a bank robbery, and many characters hold firearms throughout, only two shots are fired. The first is when Sonny (Al Pacino) shoots his rifle at a window to scare off the police that are trying to go around the back of the bank. The second and final one is at the end when Murphy (Lance Henriksen) shoots Sal (John Cazale) in the head.