Xellos decides not to argue with him, since whether he's correct or insane doesn't actually matter.
"Actually, it's not a foul," he says mildly. "By the time I'm finished with you, you'll be able to run this course with a stack of plates on your head and both hands with the asphalt covered with caltrops, banana peels, oil slicks, and black ice, with several people at once tripping you and throwing things at your head. If someone's tripping you, they're only moving ahead in the lessons. But I'd like you to stop for now, please," he addresses the universe in general, just in case someone he can't detect is listening. "Sumimasen, but we're only working on the basics today."