One thing about teaching a movie is that you begin to notice tiny details about it. Here's a fairly hard O Brother trivia contest that I wrote up last year while watching the film in class. (I'll post the answers in the comment section.)
1) Which artist from the film's soundtrack has a cameo in which she asks for a record of the Soggy Bottom Boys singing "Man of Constant Sorrow"?
2) Who performs the version of "I'll Fly Away" that's used in the film? (It's different than the one on the Grammy-winning soundtrack album.)
3) Whose translation of The Odyssey is quoted at the beginning of the film?
4) What moment in the film could be construed as a joke about Foley art?
5) Which character is speaking at a moment in the film when the sound doesn't match up with the image—when the dialogue does not fit with the character's mouth?
6) In what year is the movie taking place—and how do you know?