Continuity mistake: In this episode, Darrin announces that he doesn't like cream in his coffee. In season 2, "The Joker is a Card," Darrin likes cream in his coffee, and Uncle Arthur zaps a cow into the living room.
Other mistake: In the opening scene, Endora disappears then reappears for Tabitha. If you watch closely, just before she reappears you can see the shadow of Agnes Morehead/Endora on the wall behind the couch quickly coming back to the couch for the camera cut to recapture her.
Answer: Telstar was an early communications satellite system. Darrin, in a particularly sexist manner reflective of this era, is saying that telling a secret to a woman means it is guaranteed to be "broadcasted" to multiple people.
raywest ★