Master Ma's Wild Duck (BCR53)

KOAN:

Once Great Ancestor Ma and Baizhang were taking a walk when a wild duck flew by.
“What’s that?” asked Master Ma.
“A wild duck,” said Baizhang.
“Where did it go?”
“It flew away.“
The Great Ancestor twisted Baizhang’s nose, and Baizhang cried out in pain.
“When did it fly away?“ asked the Great Ancestor.

—Blue Cliff Record, Case 53