The early inhabitants of ireland were in fact rather fond of decapitating their foes and using the heads as decoration/trophies. But as far as the modern custom goes it was turnips since pumpkins are native to north america. The headhunting and carving iirc are different concepts though. Headhunting was partially to keep your enemys spirit energy whereas carving is to ward off evil. The prechristian irish were pretty barbaric. But i may carve my turnips early and bury them so they look like decapitated desiccated heads.
