The Firefly Bar is named as a tribute to Joss Whedon, who produced Firefly (2002), and some of the Marvel movies featuring Robert Downey, Jr. David Krumholtz, who plays the Chicago prosecutor, played the hacker in Whedon's Serenity (2005), the theatrical follow-up to Firefly (2002).
Vera Farmiga and Robert Downey, Jr. play characters who are supposed to be the same age, but she is eight years younger than him. Leighton Meester, who plays Farmiga's daughter, is just thirteen years younger than her, while Sarah Lancaster who plays Downey's wife, is fifteen years younger than him.
The fishing cabin, where the judge receives his chemotherapy treatments, is the same cabin that was used in Divine Secrets of the Ya-Ya Sisterhood (2002) (where Siddalee stays after fighting with her mother). Both movies were filmed in Wilmington, North Carolina.
There are three additional references to previous roles Robert Duvall has played: 1) The bailiff's name is Augustus or Gus....Duvall has often said that the role of Augustus McCrae in Lonesome Dove (1989) was one of his favorites. There's a bit of a gleam and a subtle smile when Duvall's character says "Gus". 2) When Sam and Hank are discussing their past at the lake, Sam uses the phrase "A more superior prick never shit between two shoes." Duvall's character in The Great Santini (1979) is described as "The greatest Marine fighter pilot that ever crapped between two shoes!" 3) Sam talks about "an offer he can't refuse", a line from The Godfather (1972), where Robert Duvall played Tom Hagen.
Before going on a bike ride, Hank Palmer changes into an old Metallica t-shirt from the "Damaged Justice" tour, circa 1988-1989. The back of the shirt features an illustration of a giant judge's gavel.
Judge Palmer (Robert Duvall), and his doctor, tell Hank Palmer (Robert Downey, Jr.) that the Judge has been undergoing chemotherapy for a year. In court, Judge Palmer states that he has been undergoing chemotherapy for six months. In a real trial, Hank, as a defense attorney, would have been obligated to correct the Judge's deliberate effort to diminish the extent of his treatment, but Hank does not do that.
Joseph Palmer says in the film, that he is seventy-two years old. Robert Duvall was eleven years older when the film was released, and became the oldest Oscar nominee ever, for his performance at the age of eighty-four.
Judge Palmer (Robert Duvall) mentions that Hank's (Robert Downey, Jr.'s) wife was "playing hide the pickle". In Avengers: Age of Ultron (2015), Tony Stark (also played by Downey) says that Black Widow and Bruce Banner are "playing hide the zucchini".
Director David Dobkin claimed, that he and Robert Downey, Jr. wanted Hank Palmer to seem as much as possible like Tony Stark at the beginning of the film, in order to play with audience expectations of the character.
The name Hank Palmer combines two heroes from Marvel and DC comics: Hank Pym and Ray Palmer, and both of them are size shifters and are scientists. Robert Downey, Jr., who plays Hank Palmer, has also played Tony Stark, a Marvel comics scientist, in the Marvel Cinematic Universe.
The scene of Hank and Joseph's reunion in the funeral home, was actually one of the last filmed. David Dobkin wanted to avoid such a scene, and to instead just show the two of them resuming their tension and bickering. But as the film was edited, Dobkin decided otherwise.
Harry Palmer, played by Sir Michael Caine, is the name of Len Deighton's spy in The Ipcress File (1965) and Funeral in Berlin (1966). (Other than similar character names, Sir Michael Caine had nothing to do with this film.)
When Hank is driving through his hometown, he mutters that things never change. All of the vehicles that are seen on the streets, are parked parallel to the street, rather than appropriately parked in their spaces.
Despite the film ending on an open note, in the Director's commentary, David Dobkin says that he is certain that Hank will become Judge of Carlinville, and hence the title of the film refers to Hank, not Joseph.