Continuity mistake: When Penny asks Sheldon "What trauma?" in the electronics store, Sheldon holds two boxes - one with an orange side on top of one with a black side. In the next shot the black sided box is on top of the orange one. The boxes then continue to swap places during the whole scene. (00:11:50)
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.
Character mistake: Raj cannot talk with a woman around, but when Leonard claims they'd have to cut him in half to play teams, he blatantly argues back, and Penny is present with them. Regardless of if he was facing her or not, he shouldn't have said anything.
The Deception Verification - S7-E2
Continuity mistake: In the scene where Howard and Raj are comparing the size of their breast area, Bernadette is seen in the background holding a mug with the handle in her right hand. However, when the scene zooms in on her, the handle appears in her left hand.
The Hot Troll Deviation - S4-E4
Continuity mistake: When Howard and Bernadette are talking in the Cheesecake Factory, her apron that she puts on the table is constantly changing position. (00:12:30)
The Hot Troll Deviation - S4-E4
Continuity mistake: When George Takei and Katee leave Howard's bedroom, in one shot Howard is clasping his hands together, in an instant they are spread out completely. With no time to move them. (00:04:25)
The Parking Spot Escalation - S6-E9
Other mistake: Sheldon tries and fails to move Howard's car at the start of the episode. However if you look closely the car does roll backwards even though the handbrake is applied.
The Maternal Congruence - S3-E11
Visible crew/equipment: When the four (Leonard, Penny, Sheldon and Beverly) are driving to the airport at the end, the studio lights are reflected in Beverly's sunglasses.
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.
Continuity mistake: During the whole opening scene, the way in which Leonard holds the letters in his hands keeps differing.
The Lizard-Spock Expansion - S2-E8
Continuity mistake: At the very beginning, Leonard's Diet Coke keeps changing position without anyone touching it.
The Pork Chop Indeterminacy - S1-E15
Continuity mistake: When Sheldon says that his sister was sent to spy on him, his arms are behind his back. Camera cuts and they are now at his side.
Continuity mistake: When Leonard and Sheldon are talking with Penny during the scene where she is being allowed to sleep on their couch, the pullstring on her hooded jacket keeps alternating from hanging loose to being caught inside the top of the jacket. (00:07:40)
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 Vegas Renormalization - S2-E21
Continuity mistake: When Leonard and Raj are getting ready in the bathroom, Raj picks up a tube of shampoo/conditioner off the bathroom bench with his left hand. However, in the next shot, Raj has nothing in his left hand and the tube is back on the bench, with no time for him to replace it between shots.
The Big Bran Hypothesis - S1-E2
Audio problem: When Penny is talking to Raj on the stairs to the apartments, during some shots we see her from behind. In one shot, we hear her say something like "And I'm freaking out", but you can tell by the way her jaw moves that she was actually saying something different. (00:14:50)
The Gorilla Dissolution - S7-E23
Revealing mistake: After Howard lets go of the unpacked treadmill, it begins to fall down the stairs. As it goes out of frame, the treadmill begins to level itself out, but the sound of it is still heard falling and Howard, Bernadette and Raj continue running past, way further than where it levelled itself out anyway. (00:00:35)
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.
The Gothowitz Deviation - S3-E3
Continuity mistake: When Penny is making French toast and Sheldon walks into shot, the edges of the toast are not covered in egg whilst the rest of the toast is. About 30 seconds later, Penny asks Sheldon if he wants French toast and the edges are still not covered in egg. The shot cuts to Sheldon. In this shot we can see Penny's hands to the far edge of screen and fully raised showing us that she hasn't dipped the edges of the toast in egg yet. But in the next shot, we can see the whole of the toast is covered in egg, including the edges of the toast that were clear a moment earlier. (00:00:20 - 00:00:50)
The Robotic Manipulation - S4-E1
Continuity mistake: When Penny says "let's just finish our dinners" she raises her fork twice. (00:16:45)
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.