Continuity mistake: When the children are singing, "So Long, Farewell", as they are going upstairs they pass a picture of Lois' parents hanging along the middle of the stairwell. When they get to the top of the staircase, we see the exact same picture, but now at the head of the stairs.
Revealing mistake: When Brian says "Well face it Peter, your attitude towards women isn't exactly enlightened", Brian's dog tag is the same color as his fur. It also stays still, even while Brian is moving his head. (00:11:10)Nikolai
Continuity mistake: After Lois says, "When Meg and Chris turned one I missed everything," it flashes back to Lois writing 'happy birthday Meg' on the cake, and there's wallpaper border at the top of the walls, but when Peter asks her what she's doing in the kitchen the wallpaper border is gone. The paper cups that Lois filled with punch also vanish, and the rolling pin, board, etc. suddenly appear. (00:11:30)Super Grover
Continuity mistake: Right after Lois is telling Peter that he should go to Joe's house, you see a plate and a coffee mug. But right after the angel spirit holds the gun up to Peter's head, and he is walking away from the table, the plate and mug are gone.Movieman123
Continuity mistake: When the black knight appears and says to Peter "What are you doing with my girl!?", there is a pitcher and a basket with a chicken leg on the table. But on the next shot where the camera is facing to Peter, both the pitcher and the basket disappear. (00:17:20)iGregory2