“What you must understand, Harry, is that you and Lord Voldemort have journeyed together into realms of magic hitherto unknown and untested. But here is what I think happened, and it is unprecedented, and no wandmaker could, I think, ever have predicted or explained it to Voldemort.
“Without meaning to, as you now know, Lord Voldemort doubled the bond between you when he returned to a human form. A part of his soul was still attached to yours, and, thinking to strengthen himself, he took a part of your mother’s sacrifice into himself. If he could only have understood the precise and terrible power of that sacrifice, he would not, perhaps, have dared to touch your blood… . But then, if he had been able to understand, he could not be Lord Voldemort, and might never have murdered at all.