When Lydia Winthrop discovers the household safe has been opened, she picks up a bracelet with her left hand and transfers it to her right hand. Then, a closeup shows her right hand with just rose petals in it and enough of her left hand to make it fairly clear she isn't holding the bracelet at all. Then, after the closeup, the bracelet is back in her right hand.
Lydia Winthrop tells Jessica that her ring has been in her family for two generations (mother-daughter), but she later says the "ring was given to [her] by [her] great-grandmother." That would make it four generations, if the ring had originally belonged to her great-grandmother.
There were never any witch burnings in New England (nor in old England, for that matter). Those accused of witchcraft were hanged, not burned at the stake. Only in Continental Europe were accused "witches" and heretics burned at the stake.
When Jessica congratulates Mariah for her impressive performance as Rachel, she refers to it as a "rehearsal" when, in fact, it was an "audition".
Jessica tells Lydia Winthrop that her stone "is an ideal brilliant cut diamond." It is difficult for a nonprofessional to identify a "round brilliant" (the standard diamond industry term) as opposed to a "mine cut" diamond after looking at it for 2 seconds indoors without a loupe (magnifying glass). Furthermore, it is not uncommon for people to replace an older diamond with a newer diamond with better clarity, color, or cut.
The Witch's Curse aired in January and the cast is wearing coats, so it's presumed to be winter. Cabot Cove is in Maine yet the foliage is all green, there are flowers blooming, no bare trees, and as usual no snow.
Louis Herthum is credited as Deputy Dave Anderson although he is referred to as Deputy Andy Broom throughout the episode.