verb · To play the lute to a cow; the literal origin of the idiom.

相传古代音乐家公明仪曾对牛弹琴，而牛却无动于衷。

expression · To waste effort or words on an audience that is unable to understand or appreciate them; to preach to deaf ears or talk over someone's head.

跟他谈论量子力学简直是对牛弹琴。