Continuity mistake: In the classroom scene where Kyle tries to be excused from class to find Ike, Cartman sets Pip on fire as he was sitting just behind him to the the left. However in the previous shots Pip had not been sitting there, some other kid was and wouldn't have had enough time between shots to move.
Continuity mistake: After Mr Garrison announces Kathie-Lee will be presenting an award for Cartman, you see the next scene in the Mayors office. There we can see cleary the curtains are red, then she looks out the window and looking in the office from outside, they are pink, but it goes in the office again and now they are back to red.
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Continuity mistake: When Mr. Garrison returns to the classroom with his new face and does the posing to "Shadow Dancing," it flashes back to the students and Wendy is dressed in her normal clothes instead of the black leather she wore to impress Stan. Next time it shows her, she's back to normal.
Continuity mistake: In the scene where Mr. Garrison is telling the students to to get in place for the play, Kenny is seen in the group. Despite the fact that he is supposed to be taking the star or the ceiling at that point. He is then seen seconds later climbing down the ladder with the star.
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Continuity mistake: When the town are protesting outside the Mayor's office, the woman at the front of the Nativity protesting group is wearing a purple shirt. A few seconds later, she is with the group against the cutting-down of Christmas trees wearing a completely different shirt (white with a Christmas tree in a red circle with a line through it).
Continuity mistake: In the cemetery scene where Kyle calls the emergency hotline and Stan and Cartman hold off the zombies, in the shot where Kyle's hand holding the Worcestershire Sauce is shown in close-up, his gloves are shown as green instead of white, which they are while Kyle is in his vampire costume.
Continuity mistake: Cartman accidentally sets Fluffy the Cat on fire. When the cat is on fire, he jumps up into the air and knocks off the picture on top of the cabinet and it falls onto the floor. When Stan, Kyle, Cartman's mom and Wendy walk into the living room in the next shot, the picture has disappeared.
Continuity mistake: When Wendy finds her report paper, it has "good effort" and her grade written in red marker pen on it, with a short note underneath it also written in red pen. In the next shot the "good effort" and grade number are still on the paper but the note underneath has vanished.