a little bird told me可不是字面意思“一只小鸟告诉我”，其实真正含义是“有人私下告诉我；有小道消息”

【例句】
A little bird told me you were mad at me yesterday.
有人告诉我你昨天生我的气。

A little bird told me we have to work overtime tonight.
有人告诉我，我们今晚必须加班。