A Flat-Earth Koan

Goofus would raise his middle finger whenever he was asked a question about Flat Earth. A novice began to imitate him - when anyone asked the boy a question about the shape of the Earth, the boy would give them the bird.

Goofus heard about this, seized him and bit off his finger. The novice cried and ran away. Goofus called and stopped him. When the boy turned his head to Goofus, Goofus gave him a double-bird. In that instant the boy realized he had wasted his life, took himself and his severed finger to a hospital that re-attached it, and impressed at the result went on to study medicine himself.

Inspired by the AI Koans and a particularly gruesome koan about a Zen teacher named Gutei or Juzhi.