I'm researching the mythology behind the Tathlum. As far as I can tell it's a magic sling bullet from Celtic myth. When was the association with exploding heads made? I see that in D&D as early as Deities & Demigods and it's spread to Pathfinder one of the APs. While the Celts were into limed head trophies, I never heard of them being weapons. Is this something D&D invented?
Just a simple connection between the two, turning a limed head trophy into a magic sling bullet (also possessing the power of Balor's eye, destroying nearby enemies).