"Well, yes -- blood's a powerful spell agent, no matter the sort. The darker the magic, the more specific they are -- at least, that's what it seems like." Yeah, Bobby's done his share of simple spells and that sort of thing to summon demons and track people when he can, but that's about the extent of his power.

"Anything that has 'vital' power, so to speak, can be used. Hair, skin, nails...that sort of thing's a bit easier and more inconspicuous to gather, if you're the baddie planning to hex your spurned lover or somethin'."