Rincewind opens his mouth to protest, then closes it, not having any idea at all what Severus meant. He swallows. "I'm truly sorry," he says humbly. And not just because there is a distinct possibility of him spending the rest of his life on a lily pad. "Um, I don't suppose I could look at your instruction book?" He asks hopefully. "I'd be very careful with it. I've had lots of experience dealing with magical books."