The Gateless Gate/Ummon's Sidetrack
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.

Afterwards another teacher, Shishin, asked his pupils: "At what point did that student go off the track?"

 Mumon’s comment: If anyone perceives Ummon's particular skillfulness, he will know at what point the student was off the track, and he will be a teacher of man and Devas. If not, he cannot even perceive himself.
 When a fish meets the fishhook
 If he is too greedy, he will be caught.
 When his mouth opens
 His life already is lost.