A certain monk had a habit of pestering the Grand Tortue (the only one who
had ever reached the Enlightenment 'Yond Enlightenment), by asking whether
various objects had Buddha-nature or not.  To such a question Tortue
invariably sat silent.  The monk had already asked about a bean, a lake,
and a moonlit night.  One day he brought to Tortue a piece of string, and
asked the same question.  In reply, the Grand Tortue grasped the loop
between his feet and, with a few simple manipulations, created a complex
string which he proferred wordlessly to the monk.  At that moment, the monk
was enlightened.

From then on, the monk did not bother Tortue.  Instead, he made string after
string by Tortue's method; and he passed the method on to his own disciples,
who passed it on to theirs.