Koans, such as What is the sound of one hand clapping and Does a dog have Buddha-nature? are concise, confusing and often contradictory sayings expressed by ancient masters that serve as the centerpiece of Zen Buddhist learning and training on several levels. First, Koans form the central component of a remarkable body of literature contained in voluminous collections produced in the twelfth and thirteenth centuries. These works include various styles of elegant poetic and eloquent prose commentaries on cryptic dialogues. The Koan compilations were greatly influenced by one of the high points in the distinguished history of the literary tradition in East Asia. The texts appealed to intellectuals in China, Japan and Korea, who sought spiritual fulfillment through interpreting elaborate rhetoric related to mysterious metaphysical exchanges.