Seeing Bellatrix again brought it all roaring back: decades' worth of stoppered hatred that Snape had never truly been able to unleash on her, on any of Riddle's arselickers, on that fucker himself.
On top of all that old homicidal fury, and the sickening knowledge that one of his students was dead, Snape knew a brand-new horror: feeling the Killing Curse reverberating through the castle's stones into the marrow of his bones, making his skull pulse around his brain, making him physically ache with the urge to curse the bitch straight to the hell where she belonged.
With an effort so intense it made his arm shake, he lowered his wand. He didn't even indulge himself with kicking her crumpled body.
He simply spat at her as the Aurors hauled her away to Azkaban