I, Darrin, Take This Witch, Samantha - S1-E1
Revealing mistake: After the hairbrush comes to Samantha, she starts to brush, and you see the lights reflect off the wires used for the gag.
Be it Ever So Mortgaged - S1-E2
Revealing mistake: When Gladys is looking through the window, you can see part of the facade cross bracing.
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 ★