Revealing mistake: When Sam and Endora are sitting on the wing of the airplane, you can see folds in the blue backdrop for the sky.
Deliberate mistake: The drunk that is always in the bar in New York is the same drunk in Salem that sees Sam twitch the witch on the signs from an old hag to a young witch resembling 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 ★