one day, the guru was sick and could not travel to his school to teach. so he gave a koan to the tortoise and asked if he would take it to his students. the tortoise agreed, because he was a good friend.
three years later, the guru was teaching a class, and the tortoise walked in. the guru was confused, and the tortoise began, “one day, the guru was sick and could not travel to this school to teach…”
you have found a lost koan.