Revealing mistake: During the scene when the people at the pool think Chris is a car sitting on the diving board, just before Lois moves out of the shot before the scene changes, her lips disappear for a split second. It's really fast but still easy to notice even without pausing or slow motion.
Continuity mistake: In the scene where Stewie is eating chocolate cake, he shoves his head in it and covers himself in cake. However when Peter walks in after having liposuction, all the cake has disappeared and Stewie is now completely clean. The bowl of grapes on the table is also gone.
Continuity mistake: In the flashback when Peter fights Ernie the Giant Chicken, Peter gets knocked off the top of an eighteen wheeler and grabs the second rung at the bottom of the truck's ladder. But when the truck driver sees the pair in his side view mirror, Peter is hanging off the top of the ladder.
Continuity mistake: After Lois accuses Stewie of peeing on the carpet, he asks her to bend down and slaps her with a glove. The glove remains in his hand in that cut, is still there when there is a wide shot of Peter, Stewie, Lois and Brian (you can just see it next to his trousers in his hand), but when it cuts back to Stewie and he starts on about "the outrages" etc, it is gone (the cut is instant, no time for him to put it back in his pocket). A common error, this one just struck me as strange, because the sandwich Stewie threw at Lois is there the entire scene.
Continuity mistake: In the scene where Lois goes down to the room where Peter is dancing, Peter is wearing blue pants. After he walks over to the door and greets her, he still has blue pants. The next shot of Lois and Peter dancing has him wearing his normal green pants, but after that it goes back to blue pants for the rest of the scene.
Continuity mistake: When Ulysses S. "Griffin" is chugging beer with Robert E. Lee, Ulysses wins. When he says "How's that Robert E. Lee," he puts the beer glass on his head. After Robert says, "Okay no more slaves, but we still don't have to read books," the glass is in Ulysses' hand. In the next shot it's on his head again.
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.
Continuity mistake: In the end of the episode whilst the families are eating lunch at the picnic table there is a lot of plates of food and glasses on the table. Towards the end of the scene Brian says "I guess some mysteries are better left unsolved", there is a wide shot after he says this and every plate and glass from the table has disappeared.
Continuity mistake: When Stewie is building with blocks, you first see a pyramid with three blocks on the bottom and two on the top. The shot changes, and he puts two more on the top, near the edge. When the shot changes again, suddenly there are five blocks on the bottom, six on the second layer, and two on the top near the middle. The letters and pictures are also all different.
Continuity mistake: When Stewie is in his room talking to Rupert and himself out loud about Janet we see that Rupert is on the left side of Stewie's pillow. When the camera pans over to Brian who overhears Stewie's musings, after Brian makes fun of Stewie the camera pans back and Rupert is gone. There is also a quick tete-a-tete on the color of Janet's eyes and the final shot is on Stewie and his crib and yet no Rupert to be found.
Continuity mistake: Just before the pest control team leaves for the Griffins', we see the black team member holding a shotgun in his hand. After showing Logan in shot, it returns to the black member and he's now holding what looks to be an MP5 machine gun. In the following shot as he starts to slide down the pole, the gun is once again a shotgun.
Continuity mistake: In 'Wasted Talent', near the end of the Chumba-Wumba song about Joe being in the wheelchair, the Chumba-Wumbas wheel Joe till he is about 15 yards away from the gate. Then as the shot cuts, Joe and the Chumba-Wumbas are standing right next to the gate. How did this happen? Nobody moved him.