あいづちを打つ aizuchi o utsu
sounds given during a conversation to show you are listening and engaged
When talking with someone, to show you are engaged in the conversation, you may nod or say things like “That’s right” or “You don’t say!”
Examples of あいづち aizuchi in Japanese are 「はい」hai, 「うん」un, 「へえ」hee, and「なるほど」naruhodo.
This idiom comes from the rhythm the blacksmith and his apprentice have when trading blows hammering hot metal. The “ai” means “together” and “tsuchi” is a hammer. “utsu” means to hit. Two people hammering hot metal require careful coordination as do people in conversation.
あの人の話は面白くなかったけれど、一応あいづちを打ちながら聞いていた。 That person’s story was not interesting, but I listened while throwing in the occasional “uh huh” and “yes.”
あの人 ano hito—that person
話 hanashi—story; talk
面白くなかった omoshiroku nakatta—wasn’t interest
けれど keredo—but; however
一応 ichi ou—for the time being