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.