“flog a dead horse”别理解成“鞭策一匹死马”，正确的含义是做无用功，做徒劳无益的事，重提已解决的事，重新引起已消失的兴趣，作无用功。

【例句】
He keeps trying to get it published but I think he's beating a dead horse.
他一个劲儿地想将其出版，但我认为他在做无用功。

There's no use beating a dead horse, Jill; he's already decided to let people smoke.
这样做徒劳无益的事是没有用的，吉尔；他已经决定让人们吸烟了。