Several times the Grinch stands on a rock outcropping by his cave that overlooks Whoville. On long shots of his cave, the outcropping is missing.
The Grinch's cave door alternates between opening to the outside and to the inside throughout the movie.
When the Grinch is talking to Mr. Bricklebaum, the ladder behind the Grinch flips. The folding joints are on the underside of the ladder and, in a quick shot, they change to the top and back down again in the next shot.
The positions of the kitchen and bedroom relative to each other change. In the beginning, Max is shown using a dumbwaiter to go UP to the bedroom from the kitchen, bringing Grinch his coffee. But after drinking the coffee, washing, etc., the Grinch sits, and the chair moves UP to the kitchen. Also, when Max exited the dumb waiter with the coffee, he was next to Grinch's bed, but when Grinch's chair goes to the kitchen, the dumb waiter is now way over to the side of his dressing room.
When we first see Cindy Lou's house, there is a long winding sidewalk that goes from her front door down into town (she sleds down it to mail her letter). In all other shots of her house, this sidewalk is missing and the road runs right by her front door.
The theme song describes the Grinch as having yellow teeth, but his teeth are white.
Right before you see all the gadgets that the Grinch has made for being able to steal Christmas, the narrator mentions in his rhyme that "soon snow would fall," but snow never falls.
When everyone in town is bringing their ornament for the enormous Christmas tree, all of the homemade ornaments have a hook for hanging except for Cindy Lou's angel.
Cindy Lou's mother explains to her it would take a month to get to the North Pole to visit Santa. Her mom then says "So, see you in a month." She should have said "see you in two months" to account for the return journey from the North Pole.