Audio problem: At the beginning of the movie when the employees start singing after Mark puts his song on, Renee Zellweger is supposed to be singing while she wipes the CDs but you hear her singing and her mouth is not even moving.
Audio problem: When Lucas goes up to Warren for the first time in the movie, Lucas makes a remark about Warren's jacket. Then Lucas whispers the fat man walks alone, Warren then turns his head away from Lucas and says "What are you, some kind of freak or something?" without his mouth moving.
Audio problem: When Warren comes back to the store with a gun and is talking to Deb, he says "My name isn't f - -ing Warren." The store employees are peeking around the wall at this. They say "His name isn't f - -ing Warren," to each other but if you read their lips they're saying "His name isn't Warren." From the Fan Edition DVD.
Chosen answer: Yes, she did all the singing for the film herself. She further demonstrates her singing abilities in the film 'Chicago'.
Padzter