Zombies in the Old World

Periodically archeologists unearth bodies with stones jammed in their mouths. This was how, we believe, people believed you kept the dead from returning as the undead. 

How did that get started? 

It probably has nothing to do with the undead. Some Irishman got a little tipsy and boasted he could swallow a rock. He put it in his mouth and couldn't get it back out.