The koan is a heart-to heart exchange between Chan teacher and student.
Chan is fundamentally inexpressible, i.e. extremely difficult to understand, measure or express in ordinary language. Chan teachers use this exchange to guide their students to find their own true heart and mind, to see into their mind of enlightenment.
Clearly, words are merely “a finger pointing to the moon”, not the moon itself. The mind is also like this. One cannot use koan to arrive at a comprehension of one’s true mind without experiencing it through concentration in meditation.
And receiving guidance from a Chan teacher and (independent) koan study are just two of the countless ways to enter Chan; even being mindful of everyday activities and happenings is Chan. To a student of Chan, everything is part of the dialogue of one’s mind of enlightenment—it all depends on the student’s attentiveness. Chan has always taught that the only path to enlightenment is the mind.
Two koans
Teacher: “Tom, Dick or Harry.”
Student: “Once I was born, who was I?”
Teacher: “Harry, Dick or Tom.”
Baizhang was in attendance on Ma Zu during one of the master’s walks, when a flock of wild ducks flew by.
“Wild ducks”, said Baizhang.
“Where’ve they gone?” Ma Zu said.
“They’ve flown away,” said Baizhang.
Ma Zu twisted Baizhang’s nose until he yelped in pain.
Ma Zu said: “Do you still say they’ve flown away?”