The Problem
The sage Vyasa had conceived the Mahabharata — the entire history of the Kuru dynasty, embedded with philosophy, mythology, ethics, and cosmology. It was too large and too complex to dictate slowly. He needed a scribe who could write as fast as he could think.
Brahma sent him to Ganesha.
The Conditions
Ganesha agreed — on one condition: Vyasa must dictate without stopping. If Vyasa paused, Ganesha would stop writing and leave.
Vyasa agreed — on one condition: Ganesha must not write any verse without fully understanding its meaning.
Both conditions were accepted.
Ganesha took his tusk — he broke off one tusk to use as a pen, so that the writing would never stop for want of an instrument.
The Dictation
Vyasa spoke without stopping. Ganesha wrote.
When Vyasa needed time to compose a particularly complex verse, he deliberately encoded it so densely that Ganesha would have to pause to understand it. Those moments of Ganesha's contemplation gave Vyasa time to compose the next section.
The 100,000 verses of the Mahabharata were written this way — in a collaboration between the sage who could think faster than speech and the god who could write faster than thought.
Ganesha's broken tusk, used as the first pen of the Mahabharata, is now one of his identifying marks.