I coulden't figure out where this went but I believe this is it. This is an idea that just poped into my head while going over a story idea that will probably never hit the net due to over planing. Also I know that in book six Riddles mortality/immortality issue is handled by the horuxies but I like this. The Dark Muncher is said to have been through many dark ritulas to make himself immortal and he is supposidly nearly there, but he wasn't all the way there when he went to kill the Potters. What if when he tried to kill Harry somehow the last dregs of his mrotality were transfered into Harry. Now an immortal Voldermort's body can't withstand the killing curse that has some how rebounded at him and so his spirit is ejected. Harry holds the last of the mortality of his greatest enemy and only by giving it back can he finally truely kill him.