He staggered back to the cauldron with Harry's blood. He poured it inside. The liquid within turned, instantly, a blinding white...

...and then erupted into flames.

As Wormtail gawked, and something within let out an unearthly scream, Harry began to laugh.

Something seemed to have broken inside him. He laughed, and laughed, and laughed, until the tears rolled down his face and he could hardly see. Even the searing agony in his scar seemed to have faded into insignificance. He could not have stopped laughing to save his life; he could pause only to breathe, and then to laugh some more.

"What's so funny?" Wormtail shouted, barely audible over the screaming of whatever lay within. "What's so funny?"

"Oh - oh, Hell," Harry managed, and then shook with another fit of convulsive laughter. He could die now. He could really die now. He would never laugh this hard again in his life, even if he lived to be as old as Dumbledore. "Did your master never tell you what happened when I met him in first year?"

He managed to blink away enough tears to see the bewilderment on Wormtail's face, which only made him laugh harder.

"My mother's love - in my skin - my blood too, I guess!" He shook his head, grinning manically. "It burns, it burns - And don't you understand? Don't you understand? You took that - deliberately! - and -"

As the shrieks of agony weakened, Harry's shrieks of laughter redoubled, and echoed through the night.

#

Author's Note: The sacrificial protection is "ancient magic" directly opposed to Voldemort and linked to Harry's blood. Which is why, when Voldemort uses Harry's blood in his resurrection ritual, it transfers to him, rather than kicking in with a vengeance.

...what?