Once Ma-tsu and Pai-chang were walking along and they saw some wild ducks fly by.
“What is that?” the Master asked.
“Wild ducks,” Pai-chang replied.
“Where have they gone?”
“They’ve flown away,” Pai-chang said.
The Master then twisted Pai-chang’s nose, and when Pai-chang cried out in pain, Ma-tsu said, “When have they ever flown away?”