Samantha's Thanksgiving to Remember - S4-E12
Continuity mistake: At the trial, the gavel changed positions between shots, you can see it moving forward and back in relation to the book. Also, the quill appears to change.
Allergic to Macedonian Dodo Birds - S4-E11
Revealing mistake: When Samantha is on the roof with Aunt Clara, her shadow is visible on the sky background... especially lower left.
Samantha's Da Vinci Dilemma - S4-E17
Revealing mistake: When Leonardo is going through the revolving door his arm/elbow goes through the frame where glass should be.
Samantha's Thanksgiving to Remember - S4-E12
Factual error: I noticed a grandfather clock when they all arrived in Plymouth (in the right corner). I won't assume this is the first Thanksgiving since the colony is built up and seems established. Plymouth was from 1620-1690s. I had to research but apparently there would not have been an ornate grandfather clock available. The first clocks were built around the time but were not common - especially in an American colony like Plymouth struggling to survive.
Birdies, Bogies, and Baxter - S4-E7
Other mistake: In the scene at the end where Baxter is saying "You learn something about how you take defeat, I never thought I would be learning something about myself" the background behind Baxter doesn't match the background when the shot is a wide shot showing the out door course, trees and buildings. Instead it looks like a painted backdrop perhaps filmed separately for the closeup. It's definitely not where Baxter is standing in wide shot.
Humbug Not to Be Spoken Here - S4-E16
Other mistake: In the previous episode, I've Got Your Nanny Right Here, Samantha tells Darrin "nobody travels by broom stick anymore. It's obsolete." She takes Mr. Mortimore to North Pole by broomstick.
Hippie, Hippie, Hooray - S4-E21
Continuity mistake: In season 4 episode 10 (That Was No Chick, That Was My Wife) Louise and Larry met Serena when Sam was explaining why she was home and not Chicago. Then in this episode neither Larry nor Louise know about Serena.
Character mistake: Samantha calls Darrin's mother "Mother Stephens" throughout episode. In most episodes, she is "Mrs. Stephens." I can't find any other episode where she is "Mother Stephens".
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 ★