Mumonkan, Koan 14: Nansen Cuts The Cat In Two

Zen Master Joshu

Nansen Osho saw monks of the Eastern and Western halls quarreling over a cat. He held up the cat and said, "If you can give an answer, you will save the cat. If not, I will kill it." No one could answer, and Nansen cut the cat in two.
That evening Joshu returned, and Nansen told him of the incident. Joshu took off his sandal, placed it on his head, and walked out. "If you had been there, you would have saved the cat," Nansen remarked.

Absurdity. Monks arguing over a cat is absurdity. No one could give an answer because the situation was absurd. Joshu meant this when he walked out with a sandal on his head.

This reminds me of a story someone I knew once told me about their final exam in an college Eastern Philosophy class. The final was a single essay question: "Explain a man standing on his head with a hat on each foot." Everyone in the class bent over their paper, furiously writing paragraphs. My friend wrote one sentence and, before the stunned class, walked up and turned in his paper. The professor read it, smiled, and declared that he had an "A". What did my friend write? "Explain a pregnant cow perched on a flagpole."

Absurdity and delusion cannot be explained and no 'answer' can be given about them. Don't waste your time.