Of course he says one more thing. And it's not even anything particularly vitriolic or cutting, it's just a last word--but Sirius is wound too tight to permit a last word; he's too ready to snap, just now, because the world isn't fair, because James is at least good and decent, and the ship's traded him out for the slimiest git Slytherin house has produced in ages--grown older and eviler, and nothing of what he's been told of the future (that Snape ends up helpful if not decent) will ever convince him to tolerate Snape.

Sirius doesn't bother with any real answer to that, though he thinks up a thousand, instantly--everything from a childish I was here first to that with slightly fouler language--but instead, he whips his wand up and swipes it, diagonally, viciously. A stinging jinx, unless Snape can block it--which he might, but it hardly matters, because he steps in as soon as he's got the spell off, intending to shove Snape down, or at least up against the wall of the lift--not that it's so great a distance; the space they're in is terribly close.