The Euclid Alternative - S2-E5
Continuity mistake: When Penny turns on to Euclid Avenue, the car behind her just vanishes into thin air. (00:03:50)
The Euclid Alternative - S2-E5
Continuity mistake: When driving down Euclid Avenue, the background is constantly changing between shots. In one shot it's a busy main street and in another it's a suburban street. (00:04:50)
The Euclid Alternative - S2-E5
Revealing mistake: When we see Sheldon and Howard on the scooter, look in the back of the mirrors to see the reflection isn't moving. Indicating the bike isn't moving. (00:07:40)
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.