And Something Makes Three - S1-E12
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.
I, Darrin, Take This Witch, Samantha - S1-E1
Other mistake: As Darrin tries to catch the moving ashtray, Samantha is smiling at the hilarity and raises a smiling glance at the camera crew. Possibly brought on by their own laughing. (00:09:49)
Answer: The original diamond and white gold heart necklace was given to Elizabeth Montgomery by her then real-life husband, William Asher, who also directed the show. She wore it in nearly every early episode. When the necklace was lost or stolen about mid-way through the series, Montgomery had two replicas made from rhinestones. She wore either one of those for the rest of the show's run.
raywest ★