He's Too Sexy for His Fat - S2-E17
Continuity mistake: Once Peter comes home with hunky muscles, Lois starts pushing the kids out of the front door. Stewie is in a wagon beside the threshold of the door, and he turns his head to look at Lois next to him as she pushes Chris and Meg outside. In the next shot, suddenly Stewie is now directly in front of the door, with Lois in front of him, and his head has turned again. (00:15:50)