fish and Zhuangzi

Zhuangzi and Huizi walked along a bridge that with the still water flowing beneath, Zhuangzi said that the fishes in the water are in pleasure becasue their leisureliness swiming .Huizi asked him," You are not that fish ,how do you know they are in pleasure?" Zhuangzi replied," You are not me,how can you know that i donot know if the fishes are in pleasure?"Huizi said ," i am not you, so i do not know your thought; in a similar way, you are not fish,so you do not know if the fishes are in pleasure neither, that's it." Then Zhuangzi said,"Let us date back to the origin, since you asked me that how did i know the fished were in pleasure, you already know that is the fact, but i know it from the bridge." That's a beautiful sophism.