Follow That Witch (1) - S2-E28
Trivia: Alice Pearce (original Gladys Kravitz) died of ovarian cancer in March 1966 before this episode aired. Abner's sister played the foil in place of Gladys, who would later be replaced with another actress for remainder of the series.
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.
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