Starring: Kaley Cuoco, Johnny Galecki, Melissa Rauch, Simon Helberg, Jim Parsons, Kunal Nayyar
Genres: Comedy
The Thespian Catalyst - S4-E14
Revealing mistake: When Sheldon goes to Penny's apartment and they do a scene study together, they both read lines from a multi-page script that Sheldon brings with him. On a couple of occasions the camera cuts to a side view of Sheldon and we get to see the page of the script that he's currently reading from. The pages are completely blank.
The Staircase Implementation - S3-E22
Leonard: Oh, screw the roommate agreement!
Sheldon: No, you don't screw the roommate agreement! The roommate agreement screws you!
Trivia: During Season 3, the producers learned of a show called "The Theorists" in the country of Belarus that was a copy of this show. A lawsuit for copyright infringement would have been pointless since the production company for "The Theorists" was owned by the Belarus government. A lawsuit, however, was not needed because when the actors and actresses found out the show was a rip-off this one, they promptly quit and "The Theorists" was cancelled.
Answer: Because Raj's selective mutism seems to be caused by women that Raj sees (on some sort of conscious or subconscious level) as a potential sexual partner. An attribute that wouldn't apply to either his sister or mother.