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George Clooney (Everett) was going to sing the song "Man of Constant Sorrow" for the film but it turned out that he was rather awful, so he ended up lip-synching the songs instead. He said "I'm not my aunt [referring to the late singer/actress Rosemary Clooney, best known for her role in "A White Christmas" (1954)]. I decided it would be easier to just do a passionate lip-sync." He was so nervous that the tapes of his singing would get out that he returned to the studio to make sure all of the evidence had been erased. The musical director of the film confirmed this but said "George is a very good singer but that style of music is very difficult and one almost has to grow up singing it in order to sing it convincingly. George did a really good version of the tune but it wasn't as good as he wanted." See more...
O Brother, Where Art Thou? (2000) - 2 major mistakes
Directed by Joel Coen, starring George Clooney, Holly Hunter, John Goodman, John Turturro, Tim Blake Nelson (add more)