Billy Flynn: Now look, I don't like to blow my own horn. But believe me. If Jesus Christ lived in Chicago today and if he had $5,000 and he'd come to me, things would have turned out differently.
In the final scene where Roxie and Velma are dancing in the concert hall, Roxie is on the right and Velma is on the left. They then turn around, and from behind (same point of view as before) they're suddenly the other way around.
Renée Zellweger, Catherine Zeta-Jones, and Richard Gere all did their own dancing and singing.