Big Bang: "I think it upsets Sheldon..."

This episode was so funny because we got a further glimpse into the world of Penny and Sheldon. After Howard's girlfriend shows an interest in Leonard's work, Penny gets jealous and goes to Sheldon hoping he will be able to teach her a bit about physics, even if only enough for her to hold a short conversation with Leonard. Their teacher/student dynamic was hysterical and, after they both realize she isn't going to truly understand it, she ends up just repeating information Sheldon fed her without understanding it, which helps her look smart for about two seconds. Good episode.