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Zhuangzi and Huizi were crossing a bridge over the river Hao.
Zhuangzi said: the fish have come out to play; this makes them happy.
Huizi said: You are not a fish. How do you know what makes fish happy?
Zhuangzi said: You are not me. How do you know that I don't know what makes fish happy?
Huizi said: I am not you. Of course I do not know you. [But] you are certainly not a fish. Your non-knowledge of what makes fish happy is total.
Zhuangzi said: Please stick to your original [question]. You asked how I know what makes fish happy. You already knew that I knew this and [still] you asked me. I know it over the Hao.
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"I know it over the Hao" makes sense because in the original language, the word "how", 安, is also the word "where".
The story comes down to us as part of a foundational text. Is it wisdom or a cheap joke?