Other mistake: At the end of a scene showing the dog, the scene is reversed (mirror image) for a moment. (00:08:50)
Other mistake: The map behind the officer is of Southern California. The series is supposed to be set in the NY tri-state area. (00:12:45)
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