Continuity mistake: When Wallace races to get crackers, check the packet's logo. When the camera angle changes it's different. (00:08:57)
Continuity mistake: The snowman hits his nose with a hammer, completely bending it in half. In the next shot it is suddenly magically straight again.
Continuity mistake: Tanya O'Tabby's dress sleeves come and go when she's speaking to Sam Spayed (Garfield) for the last time. (00:25:00)