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The Zazzy Substitution is the third episode of the fourth season of The Big Bang Theory, and the sixty-sixth episode overall.
Starring: Johnny Galecki (Dr. Leonard Hofstadter), Jim Parsons (Dr. Sheldon Cooper), Kaley Cuoco (Penny), Simon Helberg (Howard Wolowitz), Kunal Nayyar (Dr. Rajesh "Raj" Koothrappali)
Special Guest Star: Laurie Metcalf (Mary)
Guest Starring: Mayim Bialik (Amy)
Behind the Scenes