Not very many scholars or Zen masters really understand koans (Ch., kung-an). They might as well get into another profession. Their analysis of koans is always wrong because they don't understand the heart of the koan which is the hua-t'ou or watô in Japanese. I feel sorry for the beginner and especially the student who has been hanging around a Zen center for twenty years or more.
The answer to any koan becomes crystal clear when the ernest seeker understands the hua-t'ou. Literally, it means word's source. The source is the pure Mind before it gets stirred up or begins to vibrate in the form of a thought. When one can turn to the light of Mind he or she understands what hau-t'ou really means. This is Zen mastery.
In one of the oldest koan collections entitled The Blue Cliff Records (The Hekigan Roku), it has this to say about the hau-t'ou which is translated as "Pre-Voice".
The real substance of the universe, the ‘First Principle’, that which is behind or beyond the Voice or expression of ultimate truth, this ‘Pre-Voice’ [Hua T’ou] is transmitted only from heart to heart, and no matter how great or holy or advanced in Enlightenment a man may be he cannot transmit it by means of words and phrases. This Pre-Voice is not far away, it is indeed quite close to us, but unless one has had intimate, immediate contact with it—has had audience of it as one who has an audience with the Emperor—this very near-at-hand Truth will be as far off and separated from us as by thousands of miles. (tr., Shaw)
If anyone is truly transmitted to carry on the dark secret of Zen by way of koans they have had an audience with pure Mind. By seeing pure Mind they have not only seen the source of words, i.e., the hou-t'ou, but they have also seen the source of mental images as well as the source of the movement of their fleshy bodies! These masters see the very light of Mind before it appears or becomes a word in one's mind. When they lift up their leg, they know it is the pure Mind that is doing this. When they say "Mu", they recognize what is actually producing it. Ordinary people don't. They are attached to the effect called the hua-wei. If I say the Buddha-nature is "Mu" and you mentalize Mu all day, you are doing effect koans. You're not getting any place. If you come up with a clever answer it is still an effect or hua-wei. Now you are really lost.