Revealing mistake: When the Grinch is cutting Max's antler, the cut lines appear on the prongs before he actually starts to cut.
Revealing mistake: When the Grinch hits the Christmas decoration with the cue stick, the ball rolls over the Christmas tree, not under.
Suggested correction: The Grinch picks up the cane, then hits the Christmas ornament with it. The ornament goes past the Christmas tree (in front of it), then knocks the other ornaments off the tree. What is the mistake? The ornament is not supposed to go behind or "under" the tree.
The green branches (i.e. the tree) that the ornament passes over are several inches off the ground, and therefore it shouldn't have rolled over them since it's supposed to be on the ground. In the next shot, we see the ornament rolling on the ground, where it is rolling under the branches before hitting the base and jumping up the tree.
You are correct. I first thought the mistake was talking about a layering issue, where the ornament was supposed to be layered behind the tree, or something. I'm not sure how I misunderstood that, but nonetheless, you're right.