Hekiganroku - Case 53: Hyakujo and the Wild Ducks

When Great Master Ba was walking with Hyakujo, he saw wild ducks flying by.
The Great Master said, 
  "What is that?"
Hyakujo said,
  "Wild ducks."
The Great Master said, 
  "Where did it go?"
Hyakujo said,
  "They flew away."
The Great Master twisted Hyakujo's nose tip. Hyakujo cried out in pain.
The Great Master said,
  "Why flew away?"