Continuity mistake: In the wide shot of the town square after the mayor says there "is no Grinch problem here!", the yellow car that had a full cab that the red car hit is missing, and the red car's right headlight that was knocked out in the crash with the yellow car is back in place.
Continuity mistake: After Cindy thanks the Grinch for saving her, he stops at the door. He slides his hand down the glass, and it comes off the glass well below his chin level. When he turns around, it's just at his chin height.
Continuity mistake: When Lou enters the classroom, the teacher's yardstick switches position from straight up and down to flat as the shot perspectives change.
Answer: It was a rocket sleigh.