Last episode featuring George Tobias as Abner Kravitz. He had character parts in several major films of Hollywood's Golden Age but is probably best known for playing this role on 54 episodes throughout the series.
Serena is insulted by Darrin and she turns him into a gorilla.
This is one of several episodes where somebody is changed into an ape or chimp. But it is one of the weaker ones since the ape is obviously someone in a gorilla costume. Mrs. Kravitz sees the ape, which Serena turns into Darrin and back again.