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.
Revealing mistake: In several episodes, the window over the kitchen sink is shown from the outside, while snoopy people look in. The window shown in these exterior shots is far too low to be the same window that is over the Steven's kitchen sink, which is shown in many shots looking out.Super Grover
Continuity mistake: In the early shows, the door between the dining room and kitchen is a swinging door with louvers. In later shows there is a regular sized door with partial louvers. However, after this change, there are a couple of episodes within the same season, where the regular sized louver door is a solid door with no louvers.Super Grover
Audio problem: When Samantha and Darrin are at his ex-girlfriend's house for dinner, Samantha is doing all kinds of things to sabotage the dinner, even making a gust of wind come through the front door thus blowing the ex's wig off. The ex girlfriend is screaming but the screams don't match up to what her mouth is doing.
Other mistake: While Gladys Kravitz is standing in front of her house, which is across the street from the front of the Stephens' house, Gladys sees the Stephens' backyard just as Sam zaps a swimming pool and then zaps it away, but since the Stevens' backyard is located behind the house where the living room and dining room are, this would be impossible even for nosy Gladys Kravitz.
Continuity mistake: When Dave sees Darrin's ad for the community meeting, he suggests a couple of changes, one of them being to add a line saying "and bring your friends". But the ad was shown in close-up shortly before Dave's arrival, and there was already a line saying "Be sure and bring all your friends". (00:13:35)Jeff Swanson
Continuity mistake: When Sam is looking for Darrin to tell him the good news, Aunt Clara walks into the living room holding the large book with its cloth bookmark hanging over the top front of the book (facing Sam), but in the next shot the bookmark has switched to hanging over the top back of the book (facing Clara). (00:13:40)Super Grover
Continuity mistake: When Aunt Clara tells Sam not to worry about Darrin because she has her book of spells, there's a closeup of the book with its binding facing left and Clara pointing to the large title "Spells and Incantations" on its cover, but in other shots Clara's holding the book with its binding facing right (we see Vol. 7 on the binding) so the cover is facing the opposite way, and there is no title on the cover. (00:14:00)Super Grover