Someone on this list wrote:
This is a koan, a device in Zen Buddhism used by a teacher to help the student liberate themselves from being imprisoned by rational discursive thought.
Here is another koan.
A Zen student told Ummon: "Brilliancy of Buddha illuminates the whole universe."
Before he finished the phrase Ummon asked: "You are reciting another's poem, are you not?"
"Yes," answered the student.
"You are sidetracked," said Ummon.
Here's my commentary. The teacher neither agrees or disagrees with the student's statement. This is "Mu" if you wish. Instead the teacher directly observes the student's mental processes, confirms the observation, and provides helpful advice.
The teacher is not trapped by rational discursive thought. Here the teacher uses only 12 words. Sometimes a teacher uses a single word, or no words at all.
You'll find this koan and further commentary at https://www.sacred-texts.com/bud/glg/glg39.htm. -- Jonathan