Plot hole: Darrin tells Samantha that Larry thinks the Stephenses are having a costume party. While Larry earlier had said that to himself when he looked through the Stephens' living room window, he never said it to Darrin. (00:20:45)
Revealing mistake: As Larry walks up to the Stephens' house, his shadow falls across the "house" and "street" behind him, revealing that it is a painted backdrop. (00:14:45)
Continuity mistake: In Tabitha's room in an early scene, Tabitha for some reason is in her play pen in her bedroom rather than her crib as usual. Later, the crib is back when Darrin is securing her toys in the locked toy chest.
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