The Dead Hooker Juxtaposition - S2-E19
Continuity mistake: After the guys leave and Penny and Sheldon are eating alone, Sheldon's chopsticks switch between an unevenly broken pair of chopsticks and an evenly broken pair of chopsticks.
The Panty Piñata Polarization - S2-E7
Continuity mistake: When Leonard talks to Penny about having to live with Sheldon he has his hand up to his chest. Camera swaps to a side view and his hand is not in front of his chest any more. (00:07:30)
The Griffin Equivalency - S2-E4
Continuity mistake: When Raj asks the guys who's going to the party on Saturday night, Penny's grip on the martini glass she has changes between shots. (00:10:20)
The Barbarian Sublimation - S2-E3
Continuity mistake: When Penny explains she has bought the game, her grip on the laptop changes. (00:06:50)
The Barbarian Sublimation - S2-E3
Continuity mistake: At the start, after Penny has dropped one bag, there is an item in the top of the remaining bag. This item keeps appearing and disappearing. (00:01:20)
Continuity mistake: When Leslie and Leonard are talking about starting a relationship again, the can of Diet Cola keeps rotating. In some shots from Leslie's point of view you can't see the logo and in others you can. (00:06:30)
Continuity mistake: When Leonard says he is happy Penny is moving on he has nothing in his hand. Camera cuts and now he is holding a bit of bread. (00:03:00)
Continuity mistake: When Sheldon is undoing a pair of socks that Penny has paired, Penny is seen holding a single sock. Camera changes and she now has nothing in her hands. This is an instant cut. No time to drop it. (00:05:50)
The Financial Permeability - S2-E14
Continuity mistake: Sheldon opens the can with money in and puts the lid on the side, However in some shots he has the lid in his hand. (00:04:00)
The Financial Permeability - S2-E14
Continuity mistake: When Sheldon is holding the money out to Penny, the can that is being held by Sheldon is constantly moving up and down in height in relation to his shirt. (00:04:00)
The Killer Robot Instability - S2-E12
Continuity mistake: When Penny and Howard are arguing near the start, Penny has her arms crossed in one shot and down by her side in the next. (00:04:50)
The Panty Piñata Polarization - S2-E7
Continuity mistake: At the start when Howard is asking about the house, the pencil in front of him keeps moving on the table. Note the point and the edge of the table. (00:02:30)
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)
Continuity mistake: When Sheldon is looking at his socks that Penny paired up, his grip on them changes between shots. (00:06:00)
Continuity mistake: Penny throws Sheldon's sock down on the table, and their positions change when Sheldon picks them up, despite no one touching them. (00:05:50)
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)
Continuity mistake: When Leonard shows Penny the leaflet at the end, she is holding it in one hand in shot but with 2 as the camera changes. (00:19:50)
Continuity mistake: In the laundry room, Sheldon is holding a blue shirt in his hands and has a bit of extra material near his hands. When the shot changes, he is holding the shirt differently and the extra material has gone. (00:05:50)
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.