The Cooper-Nowitzki Theorem - S2-E6
Continuity mistake: When Ramona starts talking to Sheldon in the cafeteria, the way Sheldon holds his knife and fork changes between shots. (00:04:00)
The Cooper-Nowitzki Theorem - S2-E6
Continuity mistake: The way Ramona holds her drink in the cafeteria changes between shots. (00:03:50)
The Cooper-Nowitzki Theorem - S2-E6
Continuity mistake: At the start as Leonard says about being able to talk to women, he puts his hand on his drink. Camera cuts and now his hand is back by the edge of the table. (00:02:50)
The Cooper-Nowitzki Theorem - S2-E6
Continuity mistake: When Raj says there is always a catch, Leonard's hand goes from on the table to on his leg between camera cuts. (00:03:00)
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.