Isopraxism is imitation of a counter-party’s speech patters, body language, vocabulary, tempo, and tone of voice. It establishes a bond and let’s the other know that you “are the same” and therefore they can trust you. While it can take many forms, in negotiation purely verbally it can be just repeating the last few key words that the other person said1.
1. Voss, C. & Raz, T. Never Split the Difference: Negotiating As If Your Life Depended On It. (Harper Business, New York, 2016).