The Habitation Configuration - S6-E7
Continuity mistake: When Howard is almost done moving out of his mother's house, there is a table in front of him with a measuring device in the top corner. In one shot, the device moves to the opposite corner of the table. In a few shots later, the item returns to its original position.
The Habitation Configuration - S6-E7
Continuity mistake: When Wil first enters Fun with Flags, he has his flag partly on the table in front of him. In the next shot, the flag is not on the table at all.
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.