Harry sighed and prepared to relive some painful memories once again. "Bailisk fangs," he began. "Or a weapon that's infused with the venom - stabbing them seems to work. Fiendfyre. Dumbledore used some kind of spell on the ring, but we never worked that out. And the killing curse, if it's human." Of course there was only one unofficial occurrence of this, so it was hardly Horcrux Research Essay material.