Other mistake: When Stewie sneaks into his parents' room and attaches the breastfeeding pump to Lois, he places the cups too high on her chest for them to be on her nipples. You can see this, especially after he removes the cups.
Revealing mistake: When Peter leans down to get the basketball, a dot briefly appears on his shorts, then disappears almost immediately.
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 ★