"It depends," Strange answers, trying to give Alphys a reassuring smile. "Ideally it's best if one cleans their plate, but it's not terribly rude if you don't eat everything. But no matter what, at least try everything on the plate and make an attempt at eating what's offered--unless you're allergic, of course. Then politely explain and refuse."

Which again, Strange has already had to explain once before, he has so little faith in the carnival to get things done.