Disclaimer: I'm not muscling in on JK's turf - just gambolling on it, like a spring lamb, having fun working out the literary and psychological puzzles which she is having fun setting us.
"Is little baby fwightened? I'll give you something to be frightened of," Bellatrix added viciously. Behind her, red eyes glowed fitfully in the gathering darkness.
Backed against the castle door, his Protego failing, Harry stared wildly over the stone banister. He alone stood between Voldemort and the children. Snape's intervention had bought time, but Snape was down, dead or...
Peripherally, he saw Snape grope for his wand, flung fifteen feet away. They needed a distraction Voldemort couldn't magically dismiss. A storm or...
Behind the massed Death Eaters, the Forbidden Forest swayed softy. Harry raised his wand.
"Accio Blast-Ended Skrewt!"
Blast-Ended Skrewts are perpetually angry and almost immune to magic. We know there's at least one left, roaming around in the Forbidden Forest - and it must be twenty feet long by now.