At first, the Night Fury is lost to her attention. The rumble heads off into a higher direction, now sounding very much like a cat's purr. And then, sluggishly, he realizes that she spoke. He opens one eye and makes a vaguely indignant noise, which just briefly increases the volume of that purr.

But his heart really isn't in it. He's aware, if only a little, that he doesn't exactly strike fear into anyone's heart when he's imitating a feline.