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.
The Killer Robot Instability - S2-E12
Revealing mistake: When M.O.N.T.E. crashes through the door at the end, the door hits the wall on the other side of the corridor. The wall shakes, revealing it's a set.
The Killer Robot Instability - S2-E12
Revealing mistake: When M.O.N.T.E. crashes through the door, if you watch carefully, the door is already off its hinges and falling before M.O.N.T.E. hits it.
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)
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.