For a variety of reasons, I'm not going to open that can of worms. Instead I have a story which may be a Kyoto folktale, or may have been made up by Gregory Benford for his novel Sunborn. The reason I'm not sure is the very perfection of the zen-punchline; usually I'm either slightly disappointed or completely fail to get the point of zen koans. Anyway:
Two men were watching a beautiful pool and the koi fish that swam just below its calm, clear surface.
'The fish are happy,' said one man.
The other asked, 'How can you possibly know?'
'How can you know if I know?'
'How can you know I cannot?'
'That is not the point,' said the fish.