Season 4, episode 14, Sheldon asks Penny to give hom some acting lessons in order to improve his teaching. At one point, Sheldon & Penny act out a scene from a play Sheldon wrote. They each have a copy of the script that they read from through the scene. As the scene progresses, and lines are read, Sheldon periodically flips to the next page of his script as if to keep up with where they're at. He ends up turning the page 3-4 times. Problem is, Penny never flips a single page, even though she's supposed to be reading along at the same pace.