In light of the turn his musings had previously taken, Severus thought better of his first instinct, which was to quip that she ought to quake in her boots, obviously. Because if she was actually the metaphorical coiled snake, the last thing he wanted to do was the verbal equivalent of waving a limb in her face, almost daring her to strike. He might have been daring, but he wasn't reckless. That was a Gryffindor's domain, not his.
"Given that I am more likely to be the chaperone than to need one, I daresay you're safe enough," he answered, with a slight shrug. Though he made no move to enter, he did look past her, into the room, which was ... very nice, actually. He could see why she might be hesitant to leave it. "Or you could always slam the door in my face," he added, nodding inside. "Now I've seen the room, and have a good idea of where the center is, I can cast the spell just as easily from out here."