It's a stupid question, and one Severus barely lets him finish before he fires off a stunning spell - of his own design, nothing so benign as one that'd just make him flop over, but an unpleasant and painful one. Of course he's not going to try and punch Sirius back, he'd just break his damn hand. But if they're in the realm of magic, he's far more formidable: even in a confined space, he can block even rebounded spells. He just... has to make sure Sirius doesn't get near him again. Which should be great, in this little box.

Speaking of, he has no idea what button to get to get it go to back down, where the rest of his things are still on the floor. Not that he thinks he's going to have time to tackle that just yet.