"when pigs fly"的英文释义为"used to say that one thinks that something will never happen"，翻译过来就是“永无可能，绝不可能”，我们来看几个例句：

"She will come to your birthday party when pigs fly."

“她是不会来参加你的生日派对的，除非太阳打西边出来。”

"I asked my boss if I could go on a two-month vacation, he said yes, when pigs fly!"

“我问我老板能不能请两个月的假期，他说可以，等到猴年马月。”

"John asked Sarah whether she would go to the movies with him, Sarah replied that would happen when pigs fly."

“John问Sarah愿不愿意和他一起去看电影，Sarah说那永远不可能发生。”

把猪和飞翔联系起来，短语"when pigs fly"就蕴含了一丝幽默意味，经常被用来嘲讽别人的野心太大。在二战老电影《猛鹰突击团》（The Eagle Has Landed）中，当一个德国将军表明他们将很快获得胜利时，情报机关的特工告诉他 "Pigs may fly, General, but I doubt it!"

出处：头条号 @Tom实用英语