Visible crew/equipment: While Sam is defending Darrin during the trial, just as she mentions their absurd belief that if someone speaks differently it's a sign of witchery, the white chalk T-mark is visible on the floor under the desk, where Phineas is sitting. It was not there in previous shots. (00:19:25)
Factual error: When Mr. and Mrs. Stephens are driving in the convertible. In second shot, there are at least 2 tall palm trees along the road. Morning Glory Circle is supposed to be a NY town. There are no palm trees growing in NY. It's obviously shot along a CA road.
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)
Continuity mistake: Before this episode (and after as well) Darrin and Samantha give their address as 1164 Morning Glory Circle, however in this episode, when Darrin slams the door, the '9' in 192 on their address spins around to make 162, hence the angry neighbor at 162 saying that his grass was installed at the Stevens' by mistake.