The Intimacy Acceleration - S8-E16
Penny: If you were to die this evening with no opportunity to communicate with anyone, what would you most regret not having told someone?
Sheldon: So it would be today? Huh... Well, I suppose there's something satisfying about dying on my birthday.
Penny: Today's your birthday?
Sheldon: Yes.
Penny: Well that's always been a secret. Not even Amy knows.
Sheldon: Well, I don't enjoy presents. And the thought of people jumping out and yelling surprise fills me with more dread than the words "George Lucas Director's Cut."
The Intimacy Acceleration - S8-E16
Sheldon: Just out of curiosity, Penny, if this experiment does make us fall in love, would you drive me to Lake Geneva, Wisconsin, for Gary-Con? It's the only convention celebrating the life and work of Gary Gygax, the co-creator of Dungeons and Dragons.
Penny: You know what, I can honestly say if we fall in love, not only will I drive you there, I will buy you all the dragon T-shirts you want.
Sheldon: Okay, babe, let's do this.
The Intimacy Acceleration - S8-E16
Bernadette: You better find my husband's mother, 'cause one way or another we're walking out of this airport with a dead woman.
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.