When George and Stuart are asked to leave the room while the Littles and Stouts talk, George picks Stuart up in his palm and Stuart's tail hangs over the edge of George's hand. When they show the two walking out of the room, Stuart's tail is now underneath his butt and not hanging.
Mrs. Little starts the washing machine without adding detergent. It's possible that there was already detergent in the machine (since it's a front loader), but when we see Stuart in the machine for the next few minutes, the water is clear enough to be rinse water (without detergent).
At the time when Uncle Crenshaw asks for his favorite "Little" nephew at the family gathering, Grandpa Spencer is not in the group shot. After switching shots and going back to the group shot, Grandpa Spencer is there.