1. Go to the part when Torrance, Les, and Jan are picking Missy up to go to the football game.
2. When Missy asks if Courtney and Whitney are totally dike-a-del-lick, look at Torrance's mouth when she supposedly says "no". her mouth doesn't move and her teeth are completely closed.
Okay, I watched this part over and I did see her lips move, if you watch her the whole time, you will see that she says it at an angle so when she turns it doesn't look like she even opened her mouth. Trust me I know what I am talking about, look at it again and watch closely.
When they make a movie, editors have to carefully match the dialouge up to the actions. My guess is that this was not done particularly well in this scene. It is called 'being out of sync' and it happens in alot of movies.