"Blocked again and again and again until you learn to keep your mouth shut and your mind closed, Potter!" Harry Potter and the Half-Blood Prince, page 603, American Edition
In the End
In the end, it got him.
Nonverbal magic: the casting of a spell, charm, jinx, hex, or curse, silently.
The insolent boy, with his heart plainly on his sleeve, was shouting hexes and jinxes in his fervor as he and his friends fought the Dark Lord and about fifteen other Death Eaters, myself included. No, I never aimed a curse at your precious Potter, nor the know-it-all Granger, or even that moronic Weasley boy; though they already looked dead on their feet, having destroyed all six of the Horcruxes; sending a curse their way looked like it would be a blessing in disguise.
But the Potter boy was in plain sight, breathless and sweating as he dodged and deflected curse after curse, when I heard him shout out the incantation for the Shield Charm. The Dark Lord countered not a split second later with a silent Killing Curse. The Avada Kedavra. The all-too-well-known Unforgivable Curse broke through the invisible charm surrounding him and tossed him to the ground like a rag doll. The Boy Who Lived was plainly dead.
The instant after it happened, as I surveyed the hysterical glee upon the Dark Lord's face and the disbelief and horror painted upon the children's, I knew what I had to do. I silently killed the Dark Lord.
Shortly afterwards, two jets of green light identical in every fashion to the one that I had sent towards the now-mortal Dark Lord now headed my way. There was no block for the Avada Kedavra, and there was no way I could dodge either one. So I just stood there resolutely and took my due.
A/N: No, I definitely don't think that Harry will be killed by Voldy, but this scenario just popped into my head while writing another story, and I couldn't resist.