Kushibussho [classic Zen koan (small presentations of the nature of ultimate reality, usually presen (狗子仏性)
Kushibussho is one of the representatives of Zen koans.
Joshu's Dog' (also know as Zaoshou's DOG) is the case number 18 of "Shoyoroku" (the Book of Serenity). Also, it is called 'Joshu's Mu' ('mu' means nothing).
Mumonkan ["Wu-wen kuan" in Chinese: "The Gateless Gate" (48 koans collection of books)]
One Buddhist priest asked Joshu Jushin ("Zhaozhou Congshen" in Chinese).
Does a dog have the Buddhist nature?
Jusho osho (preceptor or high priest) answered.
Gotoegen [(Wu-Deng-Hui-Yuan), copies of the Zen sect historiography]
In addition, this case continued into the fourth section of Zen 'Gotoegen' which was written during Song Dynasty of China.
The Buddhist priest asked Jusho osho again.
Although it is said that every thing has the Buddha-nature, why does a dog not have it?'
Jusho osho answered again.
Because a dog has desires such as want, regret, and hate, a dog does not have the Buddha-nature.'
The Buddhist priest asked Jusho osho further.
If a dog has the Buddha-nature, why does a dog have the figure of a beast?'
Jusho osho answered further more.
Although a dog self and the other know that there is the Buddha-nature, a dog continues to commit bad behaviors, so this is the reason.'
In "Shoyoroku" of the original, it is a simple answer that 'a dog does not have the Buddhist nature.'
However, when Zen experts interpreted this case as a koan, this answer is beyond the simple two directional argumentative theories of 'have' or 'nothing.'
It should be understood as absolute nothing which is closer in concept to the Funihomon (dharma-gate of non-duality) of Yuimagyo (Vimalakirti Sutra). Because of this, later, various schools of thought considered that a word of 'Nothing' by Jusho represented the appearance of his own Buddhist nature.
By this interpretation, koans of Kushibussho became one of the representative oriental thoughts, becoming well known in the world of thought as to the typical zen mondo (Zen riddle).