McGonagall had often expressed the desire to immolate the Weasley twins for their shenanigans; in the wizarding world, being set on fire was not nearly as dangerous as it was in the Muggle world, after all. They wouldn't be hurt, just frightened and hopefully slightly inconvenienced. Although - it was sort of weird that Percy was being so flippant about this. On Halloween he'd seemed frightened, with the Norbert adventure he'd been sharply controlled; Percy's behavior now smelt dangerously of an imminent breakdown. So Ron did the only thing he could: tried to ignore it. He said, wryly, "You have been spending way too much time with McGonagall."