It's the party scene, right when Richelle, Bonnie, and Sara are getting out of the taxi. Richelle gets out and says "we should NOT be here." And then Sara gets out and says "neither should Nancy." One problem though, her mouth isn't moving with the words! ha ha! Watching this always cracks me up, it's so noticeable!
Sara was really mad and was talking through clenched teeth. If you look close enough you could see this. I could say "Neither should Nancy" without moving my lips at all, also!
There is a slip-up in this scene, the girls forget to pay for the cab. The only reason I can see to this not being a slip-up is that they have asked the cab driver to wait for them.