Zen Koans
'Koan' is a Japanese word coming from the Chinese, gong-an, that means public dictate. Later, with master Rinzai (Chinese: Lin-Chi), koan became a specialized term for Zen Buddhism (in Chinese, Ch’an Buddhism, from the Sanskrit word: dhyana, “meditation”) referring to the metaphysical, mind-blasting problems given to students to solve, such as “What is the sound of one hand clapping?” or “What is the color of the wind?”. Rinzai Zen developed a long list of more than 700 koans over the centuries to facilitate students towards reaching the meditation state of “No-Thoughts” known as Satori (Enlightenment) and to promote an intuitive towards an intellectual understanding of the world.
A koan can be thought of as a puzzle. Unlike a puzzle, a koan does not necessarily have a logical or inferential answer or solution. In fact, it may have no answer at all. The effect of a koan can be to break the student out of his “thinking” mind. Some koans can be obscure and impenetrable. Often, they are paradoxical and seem nonsensical. A koan is not an end to itself, but the means to an end. They are tools for achieving insight on a level not encountered in everyday life or catalysts for awakening one’s true nature. They often recount a debate (in Japanese: mondo) between master and disciple, where the master’s response or question is said to reveal the deep nature of things as they are. Koans are then a kind of process of negation of non-self to seeking the nature of the real Self, like the ‘neti neti’ (not this, not that) process of the Hindus.
3 examples of koan puzzles
1. One-finger Zen
Gutei’s (Chu-chi, in Chinese) favorite answer to any question asked was the raising of his finger. His little apprentice copied this, and whenever he was asked about his master’s teachings, he would raise his finger. Learning of this, master called upon the boy one day and cut off his finger. In fear and pain, the boy tried to run off, but the teacher called him to return and raised his finger. The boy tried to imitate his teacher as usual, but he didn’t have a finger any more, and then the whole meaning came clear to him.
The long and short of it is that copying is slavery. One should not follow the letter, but seize the spirit...
2. A shorter line
One day Joshu drew a line with his hand on the floor of the open courtyard and told Nan-in and Tozan to make the line shorter without touching any part of it.
Nan-in approached and stood staring at the puzzle, but he was unable to solve the problem.
Finally Tozan stepped forward and drew a longer line next to the first one, but without touching it.
Everyone in the court looked at it and agreed. The first line was definitely shorter...
3. Absence of Information
“Can a shadow travel faster than light?”, asked Takuan.
This question has no answer because a shadow is maybe able to travel faster than light, but so what? What’s actually traveling? It’s not really an object just the image of an object. It is not a violation of the special theory of relativity because you cannot transmit information using a shadow. This is one of the key points of the theory. Information can be transmitted by light, but a shadow marks the absence of light and as such no information can be transmitted. It’s like saying when you don’t speak the silence is travelling faster than sound. Silence doesn’t transmit information, but on the other hand absence of information can also be a kind of information, so... This question is absurd and irrelevant!
Koan jokes
Causality
Nansen sought to find the true nature of reality. He meditated daily in front of the fence surrounding his humble dwelling. He would look out at the world through a missing slat in the fence. Beyond his yard was a green pasture with a small herd of cattle. Every morning the cows would walk past the fence in single file on their way to graze. Every evening they would return, again in single file.
One morning after the herd had passed him, Nansen sat in deep contemplation. Suddenly, he 'saw the light', and he arose and proclaimed, “The nose causes the tail!”.
Loquatious
Two Zen Masters who had not met for ten years passed each other on the street.
The first Master said “Hello!”.
The second Master thought to himself: “He still talks too much”.

Moku: Silence. All that exists is truth itself, therefore words are not necessary. In Zen phylosophy silence doesn’t mean ‘silent mind’, but to think or act with awareness and stillness.