As she begins successfully casting the spell, the staff suggests she use the blood, to paint over the mark on her flesh, theorizing that the magical forces from the two different applications should counter each other and neutralize the spell. Assuming she does so, she'll feel a powerful, heated sensation that seems to fill her body, before suddenly fading, leaving her feeling somewhat empty and cold, as well as less confident in herself, as the beneficial portions of the succubus' magic fade away. When she wipes away the blood, the markings will be completely gone.