When the bartender asks Harper if he wants a "coonass" beer, he means a Cajun (or local) beer.
During post-production, director Stuart Rosenberg hired composer Charles Fox to do additional scoring, integrating the composer's melody "Killing Me Softly With His Song", into the movie. The song had been a #1 hit two years prior, while Fox was scoring Rosenberg's previous film, The Laughing Policeman (1973).
Paul Newman once said of the Lew Harper character in the "Paul Newman: A Life" (2009) biography by Shawn Levy: "I simply adore that character because it will accommodate any kind of actor's invention . . . It's just lovely to get up in the morning, it's great to go to work because you know you're going to have a lot of fun that day".
Lynda Carter of Wonder Woman (1975) fame did the voiceover for this film's trailer, a rarity for female actors.
According to the biography "Paul Newman: A Life" (2009) by Shawn Levy, Newman had an almost major accident while racing a Porsche at a New Orleans race-track off set during production. According to the book, Newman and a cohort were not wearing seat belts when the vehicle spun out of control. Newman said:,"For a time we rode on two wheels. Then the car went on its side but we weren't thrown out. The windshield shattered. Fortunately, it was European glass that breaks into powder on impact. We climbed out of the windshield. Neither of us was hurt. We hardly had our hair mussed. As I stood by the car, somebody slammed the door on my hand. Fortunately, the door was sprung or I would have lost the tips of my fingers. 'Open the door' I said quietly. When they did, I ran to the beer cooler and stuck my fingers in the icy water. I didn't even lose my fingernails." Incidentally, in the earlier Lew Harper movie Harper (1966) starring Newman, the make and model of Harper (Paul Newman)'s car was also a Porsche, a black-top gray/silver Porsche 356 A Speedster.