smart cookie字面意思“聪明的饼干”，真实含义是聪明的人。

【例句】
It shouldn't be too hard for a smart cookie like you to learn English well.
对你这样聪明的人来说，学好英语并不难。

When my sister was only ten years old I saw what a smart cookie she was going to be.
当我妹妹只有十岁的时候，我就知道她将来会是一个非常聪明的人。