Why do abusers want you to reconfirm what you said?

My long-distance ex boyfriend was a mental abuser. Even over the phone, he sounded intimidating. I was getting fed up and like all abusers, he said the famous phrase (in a cold, menancing tone):

''What'd you just said'?

He really wanted me to reconfirm what he already obviously heard clearly. Why do abusers do that?

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Whenever I talked about other topics unrelated to cooking, he didn't care. Yet when I was briefly suggesting how I find something unfair, there he goes with the menancing ''What'd you just said'' phrase.
Why do abusers want you to reconfirm what you said?
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