Other mistake: At the end of a scene showing the dog, the scene is reversed (mirror image) for a moment. (00:08:50)
Continuity mistake: When Rodney is at the bottom of the stairs announcing phase 1 of operation breakup is a success, Samantha is at the top of the stairs. The camera edit is really bad and Samantha jumps forward about 3 feet.
Answer: Larry had been telling Darrin what it means psychologically that Samantha gave the coat away. Larry said giving it away meant she's happy being married but if she liked the coat it means she desires to be single and carefree. So when Darrin sees the coat, he immediately thinks Samantha doesn't want to be married and the fact that she twitched it means (in his mind) she wants to be a single, carefree witch again.
Bishop73