"There was somethin' goin' on that night he hadn't counted on -- I dunno what it was, no one does -- but something about you stumped him, all right."
[...]
"NEVER!"
Harry sprang toward the flame door, but Voldemort screamed "SEIZE HIM" and the next second, Harry felt Quirrell's hand glance off his shoulder. At once, there was a terrible roar, his back felt as if somebody had started an engine on it; he yelled, stumbled forward and to his surprise, something flew past his face, trailing blood. He looked around wildly to see where Quirrell had gone, and saw him hunched in pain, looking at his fingers -- or rather, the stumps on his hand where his fingers had been.
"Seize him! SEIZE HIM!" shrieked Voldemort again, and Quirrell lunged, knocking Harry clean off his feet and landing on top of him, both hands (though with varying success) around Harry's neck, yet by that time Harry had managed to pull the heavy chainsaw hanging around his back to the front, and with a roar that was neither man nor machine but somehow both he wrenched it sideways and he could see Quirrell howling in agony.
"Master, I cannot hold him -- my hands -- my hands!"
And Quirrell, though pinning Harry to the ground with his knees, was staring, bewildered, at his own palms -- still wrapped around Harry's neck, yet no longer attached to his arms.
"Then kill him, fool, and be done!" screeched Voldemort, not caring how Quirrell would accomplish this feat without the ability to hold a wand -- maybe he would literally drown Harry in his blood -- but Harry, by murderous instinct, reached up and ground his mother's chainsaw in Quirrell's face --
"AAAARGH!"
Quirrell rolled off him, his face a mangled mess, too, and then Harry knew: Quirrell couldn't touch the blade of his chainsaw, not without suffering terrible pain --