From Method to Madness - S3-E18
Revealing mistake: After the fight between Stewie and Olivia at the concert hall (followed by their breakup), Simon tells Stewie that the act without Olivia is "over" as he turns to walk off the screen. However, before Simon is even partially out of the shot, he completely disappears. (00:18:45)
Revealing mistake: When Brian and Stewie are on the tourbus, the scenery flashing past is just the same few buildings going by over and over. (00:14:25)
Revealing mistake: When the candy tree eats the kid, the kid appears mid-screen.
Revealing mistake: When Brian tells Brooke "I understand", after he thought he was being rejected, his left ear disappears for a single frame.
Revealing mistake: During the Ozzy Osbourne scene, there is a person in the audience with no mouth. (00:16:10)
Revealing mistake: Watch closely when Brian is demonstrating orbit. The apple can be seen to go through Peter's hand a couple of times. (00:07:50)
Revealing mistake: When Peter leans down to get the basketball, a dot briefly appears on his shorts, then disappears almost immediately.
Revealing mistake: Right after the "Ghost Whisperer" cutaway, while Peter, Chris, and Lois are sitting on the couch, Chris' eyes disappear for a single frame. (00:09:10)
Revealing mistake: As Stewie is walking toward Herbert's house, he just suddenly appears mid-screen.
Barely Legal - S5-E8
Revealing mistake: Every time Cleveland's tub slides out of the house, there's never any plumbing attached to it. It just sits on top of the floor so it slides out easily. In this episode its very easy to see. (00:02:50)
Boys Do Cry - S5-E15
Revealing mistake: When Lois places Stewie on the floor whilst at the Little Miss Texas pageant, one of the girls is seen looking at herself in a mirror, only she doesn't seem to have a reflection. (00:15:35)
Boys Do Cry - S5-E15
Revealing mistake: When Peter brands the cow, no burn mark is left on the cow. (00:18:20)
Revealing mistake: At Warsaw Temple, when Mort says "my bargain hunting Aunt Flo", production initials appear next to Brian's tail.
Revealing mistake: When Stewie and Brian appear in the future and watch the Griffin family in the future, the pole of the staircase Brian is holding is differently animated to the rest of the staircase. (00:13:25)
Space Cadet - S11-E9
Revealing mistake: When Chris is giving them a tour of the shuttle, they are standing up normal. When they take off, they are still standing straight up. The shuttle goes straight up. You would be on your back at take off. They would never be able to stand straight up.
The Most Interesting Man in the World - S12-E17
Revealing mistake: When Peter is attempting to sneak into the Drunken Clam whilst keeping an eye on Stewie, Peter rips out his eye and throws it towards Stewie, though his glasses are in the way of his eye. (00:03:10)
Answer: Lacey Chabert was the actress who originally voiced Meg in early episodes. She left of her own accord due to being in school and other acting work; Seth MacFarlane has stated there was no tension with her leaving, but it makes for a handy joke for the show.
Jon Sandys ★