对牛弹琴 (duì niú tán qín)

战国时期，有个叫公明仪的音乐家，弹得一手好琴。有一天，天气晴朗，公明仪带着琴来到郊外。远处有一头黄牛正在吃草，公明仪顿时来了灵感，他摆好琴，拨动琴弦，对牛弹起琴。听到这么优美的曲子，老黄牛一点反应也没有，只管低头吃草。公明仪以为老黄牛不喜欢听这首曲子，于是就换了一首，可是老黄牛还是低头吃草，公明仪将曲子换了一首又一首，老黄牛还是不理会。

最后，老黄牛吃饱了，竟然慢悠悠地走了，公明仪失望极了。人们安慰他说：“不是你弹的曲子不好，而是你弹的曲子牛根本听不懂”。公明仪叹了口气，只好抱着琴回家去了。

During the Warring States Period, there was a musician named Gongming Yi, who played musical instruments (a traditional Chinese instrument called “lute”) very well. On a very sunny day, Gongming Yi saw a cow when he was having fun in the countryside. At once, he got the inspiration. He set the lute, plucked the strings, and started playing a piece of elegant music for the cow, but the cow just kept grazing the grass with its head down. Gongming Yi though: “Maybe the cow doesn’t like this one.” Then he played another piece of joyful music, but the cow still kept its head down to graze the grass. Gongming Yi changed the song one after another, but the cow totally ignored him.

To his surprise in the end, the cow wandered away without haze after it was well fed. Gongming Yi was very disappointed. People consoled him: "It's not because your music is bad. It is because the cow can’t understand music at all." Gongming Yi heaved a sigh and went home with his lute.

Chengyu 对牛弹琴 - Play the Lute to a Cow, is used as a metaphor, meaning “to cast pearls before the swine”. It is also used to show that the speaker has chosen the wrong audience.

e.g.

wǒ jiǎnɡdehuà nǐ yíjù dōu tīnɡbùdǒnɡ, zhè búshì duìniútánqín mɑ?

我 讲的话 你 一句 都 听不懂，这 不是 对牛弹琴 吗？

You don’t even understand a word that I said. Am I playing the flute to a cow?

tā ɡěi lónɡzi chànɡɡē, jiǎnzhí shì duìniútánqín.

他 给 聋子 唱歌，简直 是 对牛弹琴。

He is singing to the deaf. It’s like playing the flute to a cow.

māmɑ ɡěi bùdǒnɡ diànyǐnɡ de ā’yí jiǎnɡ diànyǐnɡyìshù, jiùshì zài duìniútánqín.

妈妈 给 不懂 电影 的 阿姨 讲 电影艺术，就是 在 对牛弹琴。

Talking about movie art to my aunt who doesn’t know anything about movie, Mom is like playing the flute to a cow.