Continuity mistake: In the episode when Peter finds out that he is retarded, in the scene where they are about to start shooting at each other, when Peter says, "Nobody fire at Lois. She's scared.", look over his shoulder. In the picture, Stewie is facing left. Later, when they're shooting at each other, Stewie is facing right.
Other mistake: When Quagmire is sticking his body out of the car door and yelling "Whooooooa! Whoooooooa!", look at the person in the back seat. It certainly isn't Joe, who was there in the previous shot, in fact it looks like another Quagmire. (00:05:30)Blibbetyblip
Continuity mistake: When the family is in the traffic jam there's a shot from the front of the car, and in the next shot from the backseat of the car, Peter's face (glasses and part of nose) is reflected in the rear view mirror. However, there's no rear view mirror in the first front shot or shots following backseat shot.Randy DeShong
Continuity mistake: The position of the hole on the leg of Meg's pants changes. In the scene where Meg is putting the mouse traps around Joe, the hole is on the right side. When they arrive at the house with Randy Newman and Meg is telling Peter that the Twinkee factory in Natick may not even exist, the hole is on the left side. This happens again throughout the episode. (00:10:55 - 00:12:30)