Other mistake: Samantha is reading a 4-line note from Endora. The paper is semi-transparent and in a shot from the front, we can easily see the writing through the paper. However, after the note is "twitched" into a second, shorter note, there's another shot from the front - and the lettering looks exactly the same as it did before. (00:16:40)Jeff Swanson
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.