There is a story that the Hmong once had a magnificent written language. The entire body of Hmong cultural stories and traditions was written in this language using an animal hide as a canvas. 

One version of the stories says that when the Hmong were living in what is now China, the Chinese persecuted and killed all people with knowledge of reading and writing. The last copy of the written language was swallowed by a Hmong person just before he was killed by a Chinese soldier.  Some say the stories were then written in codes hidden within the elaborate embroidery of Hmong clothing, but that everyone who knew how to read the code has now died. 

Others claim the Hmong culture was so rich that no one was up to the task of re-recording all of the stories in written form. Once the last copy was swallowed, the Hmong relied on the oral tradition of passing stories from one generation to the next.