A Koan is a story or question used to free the mind of logical perception; koans are neither obscure nor enigmatic. They are often used by teachers as a tool to let their students experience true insight.
    "A koan cannot be understood by logic; it cannot be transmitted in words; it cannot be explained in writing; it cannot be measured by reason. It is like a great fire that consumes all who come near it." (Chung-feng Ming-pen [1263-1323] quoted in Miura and Sasaki 1966:5)

A Collection of Koans:
One  Two  Three
Four  Five  Six
Seven  Eight  Nine
Ten  Eleven  Twelve