A Research Study and Czechoslovakian Wedding Pastries - S2-E5
Continuity mistake: When driving back from the second study, Missy is looking out of the window when Mary says something about going out to eat. When the camera angle has changed to show the whole car, she is now looking past Sheldon into the car. (00:15:40)
A Crisis of Faith and Octopus Aliens - S2-E3
Continuity mistake: Towards the end of the episode, Mary takes a slice of pizza and takes a bite, holding it with two hands. When the shot changes to an over-the-shoulder shot from behind Mary, you can see her left hand has no pizza in it, unlike the shot from the front. (00:15:30)
Answer: Some people just have a dislike for someone that can't be explained. Could be as simple as the way he's dressed.