Sometimes, when the other person can’t hear and says, “Huh? What did you say?” real people don’t repeat themselves. They say, “Nothing. It’s not important. Never mind. I’ll tell you later. Forget it.”
Sometimes, this leads to bickering.
This technique is especially effective if a character has just said something vulnerable. People will rarely repeat something embarrassing or hurtful or vulgar. You can draw attention to their vulnerability by having them refuse to repeat themselves.
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