The Skank Reflex Analysis - S5-E1
Continuity mistake: At the start of the episode, Raj's Sirkist can rotates itself on the table.
The Good Guy Fluctuation - S5-E7
Continuity mistake: Leonard refuses Penny's offer of a glass of wine because the sulphates in wine give him migraines. This makes no sense - we have seen him drinking wine in too many episodes to count without him once complaining of an adverse reaction.
The Shiny Trinket Maneuver - S5-E12
Continuity mistake: Howard, Leonard and Raj play Jenga in a strange sort of way. Most notable is the playing order, 1. Howard, 2. Raj, 3. Raj, 4. Leonard, 5. Howard. When it's Leonard's turn he doesn't move any bricks, only pokes the tower and it's then Howard's turn. When its Raj's first turn he puts a brick on the top of the tower. When it's his turn again, the brick is gone and he puts a new one in its place.
The Russian Rocket Reaction - S5-E5
Continuity mistake: Bernadette holds her wine glass in her left hand, holding it from the base of the glass; in the next shot she's drinking from her right hand holding the top of the glass and in the immediate next shot she's once more holding the glass from her left hand. (00:14:40)
The Werewolf Transformation - S5-E18
Continuity mistake: When Penny is giving Sheldon his haircut, she accidentally shaves the back of his head. The clippers are going from the bottom of Sheldon's hair, up to the top of his head. When Sheldon goes to leave the room, it can be seen only four or five inches from the back of his head have been shaved off.
The Countdown Reflection - S5-E24
Continuity mistake: After Howard and Bernadette are pronounced husband and wife, when they kiss the camera angle switches to an overhead shot, but as it zooms out (to a digital image) things change - such as the configuration of the rooftop, or things move - such as the cable dishes, or things even vanish - such as air-conditioning units.
The Hawking Excitation - S5-E21
Continuity mistake: When Sheldon is trying to convince Howard to let him meet Stephen Hawking, Howard places a water bottle on the table he is sitting in front of. In the next shot, it appears in his hand again.
The Launch Acceleration - S5-E23
Continuity mistake: In the scene where Sheldon is scooping spaghetti onto his plate, he pauses with the spoon in the serving dish. Shot cuts to Amy and the spoon is still in the serving dish. When shot cuts back to Sheldon the spoon is being held over his plate. Shot cuts back to Amy and the spoon is back in the dish.
The Rothman Disintegration - S5-E17
Continuity mistake: After Amy returns to the apartment for the Grease DVD and discovers Penny doesn't like the painting, she then exits the apartment with the painting and the DVD with her. When Amy says to Penny she doesn't need her pity, the DVD is placed above the hanging string of the painting. In the next shot, as she walks into the hallway, the DVD is suddenly almost half below the string.
The Countdown Reflection - S5-E24
Continuity mistake: Penny mentions that she knows lots of people who got married in Las Vegas. In episode 7/9, she discovers that her "fake" wedding to Zach in Vegas was real.
The Ornithophobia Diffusion - S5-E9
Continuity mistake: When Leonard and Penny are at the movie theater the same couple walks behind Leonard, twice.
The Countdown Reflection - S5-E24
Continuity mistake: Near the beginning of the episode, Howard said the launch was on the Friday before his planned wedding. They decide to marry before he launches, and they say they only have two days. Then he tells the clerk at City Hall that he launches on that Sunday. Too many inconsistencies.
The Hawking Excitation - S5-E21
Continuity mistake: When Howard and Bernadette are in his bedroom, there is a bottle of Vitamin Water to Howard's left. In one of the shots, the bottle has completely vanished out of frame, but returns in the next shot.
The Hawking Excitation - S5-E21
Continuity mistake: Penny is talking to Sheldon in the laundry room and places a box of detergent on the machine. The side of the box is facing her. In the next shot, the box has turned to face her.
The Russian Rocket Reaction - S5-E5
Continuity mistake: In the scene where Howard and Bernadette are about to have sex and Bernadette leaves to "brush her teeth", Howard stretches and lays on the bed uncovered. After Howard's mother yells "over my dead body my son goes to space" and Bernadette appears again and says "I'm ready", then it flashes back to Howard and he is instantly covered up.
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.