CBS

Season 4: Episode 10 - The Alien Parasite Hypothesis

The Alien Parasite Hypothesis: ­While out at dinner with Penny and Bernadette, Amy Farrah Fowler meets Zack, Penny's ex-boyfriend. Much to her surprise, she finds herself flushed with an elevated heart rate and a tingling sensation. She and Sheldon discuss her symptons and she discovers that she was sexually aroused. Uncertain of what to do, Sheldon asks Penny for advice and convinces him that indeed there is something Sheldon can do for a horny Amy Farrah Fowler. He accompanies Amy to a bar where she propositions Zack but when Zack is utterly confused by the language she uses, Amy decides to abandon her assignment. When Zack shakes her hand to say goodbye, she gets what she needed and tells Sheldon she can move on.

Meanwhile, Howard and Raj argue over who would be the superhero and who would be the sidekick between the two of them. Much to Leonard's annoyance, they decide to settle the matter with a wrestling match that seems to go on forever since neither one will make the first move.