A Nice Little Dinner Party - S1-E19
Continuity mistake: The train shown is pulled by four diesel locomotives, "A" unit leads with two "B" units sandwiched between a second "A" unit. When Mrs. Stevens pulls the emergency stop cord, which would not likely be on a long distance passenger train, the locomotive shown doing an emergency stop is a steam one. Not to mention that by the time of this episode steam engines were obsolete, and less likely to have been employed, especially in passenger service.
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.
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