Angling for the book on the nightstand, Luna held it out. "If an incubus feeds off a vampire, his desires will be sated for a long time, but his empathy will all but vanish. He will become egoistic and unfeeling until he feeds from another source, which is not likely since the vampire's lust is quite potent. I remembered reading about it a year or so ago but wanted to double-check before bringing it up. It won't be a problem now since Harry flooded your system with energy from the castle."