So again, they both know that someone in the room has a pink hat on their head: it is mutual knowledge that there's a pink hat in the room.

但是他们都知道,至少有一个人戴着粉色帽子,至少有一顶粉色帽子是相互知识

耶鲁公开课 - 博弈论课程节选

I saw an old lady wearing a big classical hat today.

今天我看到一个年迈的女人戴着一顶很大的复古帽子。

英国皇家赛马会 - SpeakingMax英语口语达人