A monk asked Master Chao-chou, "Has a dog the Buddha Nature or not?"
Chao-chou said, "Mu!"
Buddhism can be a veritable mine-field of intellectualism and concepts. Koans (or problems or enquiries) were an attempt at one point to directly undercut the need for discourses and rather directly point at the truth of things via directing the mind.
This particular koan stumped me for years. It has that effect if one effectively cuts off all conclusions coming from intellectualising and analysis in attempting to 'work things out'. There is nothing wrong with using the mind, however, the mind coming to a contrived conclusion and sitting self-satisfied in a concept IS the problem.
After "seeing" happened, this koan re-appeared in my consciousness one day while sitting in the park having a smoke.
Its resolution or rather pointing was then so obvious.
How can there be any difference whatsoever in the body-mind mechanism of a human (which reputedly 'has Buddha Nature'), and a dog body-mind mechanism (which reputedly did not)?
Does Buddha Nature lie within an object, without, everywhere or nowhere?
And finally, if Joshu or Chao-chou's response was merely a pointer, rather than an answer? (And that pointer was pointing to the experience of emptiness ('Mu'), and thus the experiential understanding / knowing of the former part of the koan).
Though, that's jumping the gun, and the intention of designer of the koan (like any other koan), was probably that the practitioner would hopefully catch their "self" working very hard on this problem, and in the natural, open seeing of "their self" or lack of inherent existence thereof, the impersonal experience emptiness would ensue.