- The Cast Showoff: Not just singing, but also composing. Nearly all of the songs were composed by the two stars. Hansard wrote 7 of the songs (8 if you count "Broken Hearted Hoover Fixer Sucker Guy"), Irglova wrote two, and two Hansard and Irglova composed together. "Falling Slowly" is the only song they both composed together and sang together in the film.
- The lead singer of "Gold" in this film is also its composer, Fergus O'Farrell.
- Enforced Method Acting: The scene when Girl tells Guy "I love you" in unsubtitled Czech was ad-libbed. Guy's look of confusion is genuine.
- The opening chase scene also qualifies; they shot without permits, so when the heroin addict runs off with Guy's money, a pedestrian wound up injuring the actor by trying to stop what he thought was an actual robbery.
- Reality Subtext / Romance on the Set: Hansard and Irglová were indeed falling slowly.
- They didn't last as a couple. They broke up in 2008 while touring as The Swell Season, although they remain friends. Their 2009 album Strict Joy is about the end of their romantic relationship.
- Throw It In!: "Broken-Hearted Hoover-Fixer Sucker Guy" was just Glen Hansard goofing off between takes. Much to his surprise, it wound up in the final cut — and the soundtrack. And now, that ad-lib gets its own listing on the Broadway soundtrack.
- Irglová's line, where she says "No, I love you," in Czech, was also an ad-lib, and Hansard's look of confusion is genuine.
- What Could Have Been: Cillian Murphy was originally slated to play the Guy and the Girl was supposed to be a little older than him. But John Carney had trouble finding an Eastern European singer/actress of the right age, so Glen Hansard (hired to provide the songs and anecdotes on being a busker) suggested Irglova (whom he was just starting to collaborate with). But when she was cast, Murphy backed out of co-starring with an unknown non-actor as well as the octave-stretching music range, so in desperation, Carney asked Hansard to play the Guy.
Trivia / Once