Rats!

Once, a great and mighty chief of ours had three grandsons.  One day, their grandfather interrupted their play.  "Please, go catch this rat that I saw!" he told them.  So the three boys began to search for the rat.

But while they were searching, they were suddenly unable to understand each other.  The youngest boy could not understand the other two, the middle boy could not understand the others, and the eldest could understand neither of his younger brothers, for each spoke a unique language.  It is said that the boys grew up and started clans, each under his own tongue.  Thus were born the Lamyang, the Thado, and the Manipur tribes.

-From the Kukis of Assam