I have a couple of questions for a fic I'm writing, regarding that scene, described in the chapter "Seen and Unforeseen," in OOTP, in which Harry uses a Shield charm during Occlumency lessons and accidentally catches glimpses of Professor Snape's thoughts: "A greasy-haired teenager sat alone in a dark bedroom, pointing his wand at the ceiling, shooting down flies..." (p. 592, OOTP American hardcover edition).

Obviously the main point is that he's lonely and bored and, given the dark bedroom, probably at least a bit depressed, and given the flies, probably lives somewhere a bit squalid. But on a more picky detail question: I don't know whether there are any answers to this, but one of my wonderful betas and I were discussing it, so I thought I'd see whether anyone else has an opinion on this question:

What spell do you think he's using to shoot down those flies?

Impedimentia would work. So would Avada Kedavra, but it's an Unforgivable. is it Unforgivable when you use it like a fly swatter? And I'm sure there are other possibilities-- Petrificus Totalis, for starters. There's probably quite a list. Any thoughts? Would someone who doesn't hang out with proto-Death Eaters use Avada Kedavra on bugs?

Then there's the issue of underage magic-- either he's 17+ and he's allowed to use magic at home (he'd still probably look like a teenager, I'd imagine), or he's younger and the Trace doesn't work at his house because his mother is a witch, and she either doesn't know or doesn't care or (given the context) actually encourages it.

Anyway, just curious as to what spell you think he might be using. I'm of two minds about it, myself, so I'd be grateful for any opinions on whether that looks like an Unforgivable and whether they're Unforgivable depending on context. Thank you!