Continuity mistake: In the episode "Cat Orgy" when Sheily's boyfriend, Sklar, are playing the song for Sheily while Cartman is hanging on the coat rack you can see of what looks like a picture of Cartman's grandparents hanging on the wall. But when Sheily walks over and flings Cartman up into the ceiling for arguing with her, look at the wall, the picture is completely gone.
Continuity mistake: Just before Cartman sends his kitty out of the window with the photo, there's a photo frame on his desk and a "Cartman" cutout tacked above the desk, and on his bed is his frog toy and his hat. When Cartman walks over to the window with the kitty, all these items have vanished.
Continuity mistake: When Cartman is playing "Wild Wild West" with his toys, he has a female doll tied to a piece of wood on his bedside table. Then after his mom comes in and leaves again, Cartman starts dancing, and suddenly the doll has appeared behind him, and is also off of the wood.