When the sock puppet is playing the bells at the talent show, some of the bells ring before he picks them up.
The legs of the actor playing "The Worm" are visible in a few shots, most notably when Rick presents the bag of macaroons.
On the plane, when the troll gets knocked over to the plane door and he accidentally opens it and flies out, you can see the white curtains used to appear as sky flapping about.
When Ricky leaves Skuggs' den with the very important clue, he is walking on the dolly track, which can be seen toward the end of the shot.