The Lizard-Spock Expansion - S2-E8
Continuity mistake: At the very beginning, Leonard's Diet Coke keeps changing position without anyone touching it.
The White Asparagus Triangulation - S2-E9
Continuity mistake: When Sheldon is in Penny's apartment trying to get her to tell him why her relationship with Leonard failed, the yellow tee-shirt on the red pillow next to him keeps changing position.
The White Asparagus Triangulation - S2-E9
Continuity mistake: When Sheldon, Raj and Howard are talking in the cafeteria, Sheldon's drink keeps moving position.
The White Asparagus Triangulation - S2-E9
Continuity mistake: When Leonard is helping Sheldon open the jar, the red napkin which he left on the couch where he was sitting changes position or vanishes in every shot.
The White Asparagus Triangulation - S2-E9
Continuity mistake: When Sheldon is questioning Raj and Howard in the cafeteria, the bottle of water is on Raj's tray faces the camera with the barcoded side. But in one closeup it rotates to show the logo-branded side.
The White Asparagus Triangulation - S2-E9
Continuity mistake: When climbing the stairs at the start, Penny and Sheldon turn the corner and carry on the conversation. Camera cuts and now they turn the corner again and continue their conversation without breaking it.
The Vartabedian Conundrum - S2-E10
Continuity mistake: When Leonard and Penny are talking in the dryer room, the size of the towel Penny is folding keeps changing. (00:15:00)
The Vartabedian Conundrum - S2-E10
Continuity mistake: When Stefanie and Leonard are talking in bed towards the end, Stefanie's arm moves from on her head to on her pillow instantly. (00:16:30)
The Vartabedian Conundrum - S2-E10
Continuity mistake: When Sheldon is talking via the laptop, the amount of letters in the words he says is different to the amount of keys hit.
The Vartabedian Conundrum - S2-E10
Visible crew/equipment: When Sheldon and Leonard are making breakfast, stage lights are reflected off a milk bottle.
The Vartabedian Conundrum - S2-E10
Continuity mistake: When Sheldon is told that he can't talk, he goes from sitting to standing instantly.
The Vartabedian Conundrum - S2-E10
Continuity mistake: When Stephanie asks Leonard why he hasn't told her about Penny, he spills some of the pancake mixture out of the bowl he is stirring. In some shots the spilled mixture vanishes and the appears again.
The Vartabedian Conundrum - S2-E10
Continuity mistake: When Leonard, Raj and Howard are talking about Leonard's new trousers, the items on the tray behind Howard keep changing.
The Bath Item Gift Hypothesis - S2-E11
Continuity mistake: When Penny takes a drink from the egg-nog carton before kissing Leonard on the cheek, between shots the logo-branded label changes which direction it faces in her hand. (00:16:45)
The Bath Item Gift Hypothesis - S2-E11
Continuity mistake: When Leonard gives Penny her christmas gift, as she unwraps it she tears the paper off so that most of the box is exposed. In the next shot much more of the wrapping is back intact and differently positioned. (00:19:40)
The Bath Item Gift Hypothesis - S2-E11
Continuity mistake: When Sheldon emerges with all of the bath item gift baskets for Penny, he drops them on the floor and chair. Between shots one of the baskets on the chair changes from being an upright green-ribboned basket, to a toppled-over white-ribboned basket. (00:19:50)
The Bath Item Gift Hypothesis - S2-E11
Continuity mistake: Near the start, when the camera is on Raj, David Underhill is seen in the top left-hand corner of the screen shaking someone's hand, already in the cafeteria. Then, when the camera is on Wolowitz, David is just walking into the door of the cafeteria. David sits down to the right of the man sitting at the table, then shortly afterwards David is now sitting where the other guy was, originally.
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 Killer Robot Instability - S2-E12
Factual error: M.O.N.T.E. would not be able to knock down the door as he does at the end.
The Killer Robot Instability - S2-E12
Revealing mistake: Near the end of the show, the big robot is chasing the other robot down the hallway. The camera starts to zoom in as the robots come by it. The big robot stops just before the camera zoom is past it, yet they keep running down the hallway like the robot is still going.
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.