The Alien Parasite Hypothesis

Amy crushes on one of Penny's dim ex-boyfriends, Zack. Raj and Wolowitz argue over who'd be the better superhero.

TV-14-DL
Season 4 | Episode 10
Cast

Jim Parsons

as Sheldon Cooper

Johnny Galecki

as Leonard Hofstadter

Kaley Cuoco

as Penny

Simon Helberg

as Howard Wolowitz

Kunal Nayyar

as Raj Koothrappali