Kutasloka

Verses (Sloka) woven into the Mahabharata by Vyasa, the secret (Kuta) of which even Ganesha, who wrote it for him, could not decipher.

How Mahabharata was written
http://hindumythologyforgennext.blogspot.com/2011/10/how-was-mahabharatha-written_14.html