..."A dog, Buddha-nature" - there is no need for "nature." "A dog is Buddha" - "is" is superfluous. "A dog, Buddha" - still redundant. "Dog!" - that's is enough! Or just "Buddha!" You have said too much when you say "A dog is Buddha." "Dog!" - That is all. It is completely Buddha.


Yasutani
The Commentary on Mu
The Three Pillars of Zen, p.87