Plot hole: Mrs. Kravitz, while standing in the Stephenses' front doorway, sees Santa Claus and assumes that it's Darrin in costume. However, the very next shot shows Santa exiting the kitchen (around the corner from the front door) and starting up the hallway toward the living room. There is no possible way Mrs. Kravitz could have seen him when she said she did. (00:09:30)Jeff Swanson
Revealing mistake: The hallway that leads to the den and the back door of the kitchen has a door at the end of it, when this door is opened we see what looks like pine trees and mountains, we know that the Stevens have neighbors on that side of the house, so that when the door is opened you can blatantly tell that it is a picture.