Burt Reynolds broke his coccyx while going down the rapids when the canoe capsized. Originally, a cloth dummy was used, but it looked too much like a dummy going over a waterfall. While Reynolds recovered, he asked, "How did it look?" Boorman replied, "Like a dummy going over a waterfall."
Billy Redden, the boy with the banjo, liked Ronny Cox and hated Ned Beatty. At the end of the dueling banjos scene, the script called for Billy to harden his expression towards Cox's character, but Billy couldn't pretend to hate Cox. To solve the problem, they got Beatty to step towards Billy at the close of the shot. As Beatty approached, Billy hardened his expression and looked away.
When John Boorman was looking for an actor to play the toothless murderous hillbilly, Burt Reynolds suggested Herbert 'Cowboy' Coward, who had no front teeth, was illiterate, and stuttered. Reynolds had worked with Coward in a Wild West show in Maggie Valley, NC.
Billy Redden didn't know how to play banjo. To simulate realistic chord playing during "Duelling Banjos," another boy, a skilled banjo player, played the chords with his arm reaching around Redden's side while Redden picked. Musicians Eric Weissberg and Steve Mandel play on the soundtrack.
According to Turner Classic Movies, John Boorman wanted Lee Marvin and Marlon Brando to play Ed and Lewis, respectively. After reading the script, Marvin said he and Brando were too old, and suggested that Boorman use younger actors instead. Boorman agreed, and cast Jon Voight and Burt Reynolds.
The rape scene as originally scripted consisted mainly of swearing. The "squeal like a pig" phrase was an attempt to "clean up" the scene for TV viewing. John Boorman liked the "cleaner" version, and used it in the film.
John Boorman wanted Vilmos Zsigmond as director of photography because he'd famously filmed the 1956 Soviet invasion of Hungary. Boorman reckoned that anyone who had filmed under the threat of Russian tanks and guns would be ideally suited to an intensive and grueling shoot, which Deliverance (1972) promised to be.
Jack Nicholson had agreed to play Ed as long as Marlon Brando played Lewis. However, the actors' combined fees added up to more than $1 million, half the movie's budget, forcing director John Boorman to cast cheaper actors.
When John Boorman first tapped Jon Voight to appear in the film, the actor was at a low point. His previous film, The All-American Boy (1973), was deemed an unsalvageable mess. Convinced his career was over, Voight credited Boorman with saving his life, then spending the next few months trying to kill him with extreme stunts during filming.
The cliff climbing scene was shot during the day, and underexposed with a bluish tint added in post-production. "Day for night" shooting was common until the late 1970s because of slow film stocks and anamorphic lenses that didn't let in as much light as spherical lenses, requiring a lot of lights.
The movie was shot primarily on the Chattooga River, which divides South Carolina and Georgia. Additional scenes were shot on the Tallulah Gorge in Georgia, Salem, South Carolina, and Sylva, North Carolina. Shots of the town which did not call for the actors to be present were shot in Monaca, Pennsylvania.
Emory University Chemistry professor Claude Terry consulted on the canoe trip and navigating the Chatooga and other rivers. After the movie's release, Claude founded Southeastern Expeditions, which provided raft trips with trained guides on whitewater rivers. Rafting the Chatooga, the Ocoee River in Tennessee, and other whitewater rivers has become very popular, especially in the summer. Claude is now retired.
John Boorman's gold record for the "Dueling Banjos" hit single was later stolen from his home by Dublin gangster Martin Cahill. Boorman later depicted the crime in his 1998 film about Cahill, The General (1998).
Don Wayne Reno and Arthur Smith are credited with the first recording of "Dueling Banjos" (also known as "Feudin' Banjos" and "The Battle Of The Banjos"). Prior to "Deliverance" both parts were played with banjos, at the same speed all the way through. Almost all modern bluegrass bands play the "Deliverance" version in the key of G. In the movie both the guitarist and banjo players play it in the key of A.
The infamous "squeal like a pig" rape scene was somewhat improvised. The novel and original screenplay detailed the rape with no porcine lines. Beatty later claimed credit for the pig idea. Christopher Dickey, son of author James Dickey, stated in his book "Summer of Deliverance" that the a crewman suggested the line.
An alternate ending was shot, but cut from the final version. It takes place a few weeks, perhaps months, after the main events. It appears in author/screenwriter James Dickey's original script as part of the final dream sequence, but not as the story's literal conclusion. Lewis walks with a crutch (in Dickey's screenplay, his leg is amputated below the knee). Ed, Lewis, and Bobby meet with Sheriff Bullard near the dam in Aintry. The sheriff directs them to a body on a stretcher, then uncovers it so they can look at its face. No identifiable details of the body are shown, a deliberate choice to make the audience uncertain whether the dead man is Drew, Don Job, or the Toothless Man. The body was played by Christopher Dickey, James Dickey's son, who writes about the scene in his memoir, "Summer of Deliverance", and even he doesn't know whose body it was supposed to be. In the screenplay, Ed awakens from the dream, terrified, just before the corpse's face is revealed.