双语常用典故： Cast pearls before swine 对牛弹琴;明珠暗投;白费好意

To Cast pearls before swine 的意思是“珍珠投在猪猡前面”。swine 是个旧词，书面词，即今为 pigs,不过 swine单复同形，本句为复数。

这个成语源自《新约。马太福音》第 7 章：“Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you”. 由 于 to cast pearls before swine, 比喻确切，在后世不断引用中而成为一个国际性成语，常用来表示to offer sth valuable or beautiful to those who can't appreciate it; to give what is precious to those who are unable to understand its value 等意思，含有轻蔑嘲笑色彩。按其字面意义，这个成语与汉语成语“明珠暗投”相似，但是寓意不同，基本上不对应；按一比喻意义， 它相当于“对牛弹琴”，“向驴说经”“一番好意给狗吃”“狗咬吕洞宾，不识好人心”等。

Eg .She read them Shakespeare, but it was casting pearls before swine

I won't waste good advice on John any more because he never listens to it. I won't cast pearls before swine.