Zen Master Kyōgen Chikan was once asked by a monk, "What is the Way?"
The Master answered, "The singing of dragons among withered trees."
The monk replied, "I don’t understand."
The Master said, "Eyeballs in a skull."
Later, there was a monk who asked Master Sekisō, "What sort of thing is 'singing of dragons among withered trees?'"
Sekisō replied, "A trace of joy still being retained."
The monk then asked, "What is that thing about 'eyeballs in a skull?'"
Sekisō replied, "A trace of consciousness still being retained."
There was also a monk who asked Master Sōzan, "Just what sort of thing is 'singing of dragons among withered trees?'"
Sōzan replied, "Its bloodline has not been severed."
The monk then asked, "Well, what is that thing about 'eyeballs in a skull?'"
Sōzan replied, "Dryness without limit."
The monk then said, "Oh, I don’t know about that! Can anyone hear it?"
Sōzan replied, "There is not one person on the whole of the great earth who does not hear it."
The monk retorted, "I’m not convinced. What verses does a dragon sing?"
Sōzan replied, "Even without knowing what those verses are, those who do hear it bemoan the fact that others do not."
These three dialogues between Zen Master and monk make up the 28th Case in the Shinji-shobogenzo (Dogen's collection of kōans). The specific words are my composite interpretation of three different translations (Gudo Nishijima, John Daido Loori, and the Rev. Hubert Nearman of Mouth Shasta Abbey). As far as I know, this particular kōan appears only in the Shinji-shobogenzo and Chapter 65 of the Kana-shobogenzo - it does not appear in The Mumonkan (The Gateless Gate), the Blue Cliff Record, the Book of Serenity, or any of the Transmission of the Lamp records.
In a very helpful footnote, Rev. Nearman notes, "These three short dialogues are typical of many kōan stories that involve a Master and someone identified only as a monk. The monk — presumably a novice — asks a question based on an attempt to understand some saying by an Ancestor from a commonplace, literal perspective, whereas the Master gives a response as if the monk had asked his or her question from a spiritual perspective. This is done to help the monk break through a dependence on worldly ways of thinking. That is, in the above three cases the monks think that what they are quoting is somehow about mythical creatures called dragons, whereas the Masters are pointing the monks to a deeper meaning of the term 'Dragon', that is, they are pointing to one’s innate Buddha Nature."
Nishijima explains that “withered trees” or “dead trees” in Buddhism symbolize the vivid state of non-emotion, or people in the vivid state of non-emotion. The zazen hall of a Buddhist temple is sometimes called koboku-dō, “The Withered Tree Hall.” "Withered trees" are a common Buddhist metaphor for someone who has reached a deep level of meditation, a person whose passions have all but disappeared. This meditative state is not to be confused with a quietistic or blissful condition, which is simply a passing phase that may arise in spiritual practice.
Putting this all together, then, and setting all poetry aside, the novice monk asks Kyōgen, "What is the Way?," a question asked in many different kōans with many different answers. Kyōgen attempts to help the monk to realize that the Way is the direct expression of one's Buddha Nature through the dropping away of body and mind in zazen. The monk does not understand, as he is still clinging to the common perception. He is like a pair of eyeballs in a skull - seeing but not comprehending.