"Closest they can get to transfiguration, I suppose," he shrugs. "Or to invoking Mercury. It's a malleable substance. I recall him shrieking about scruffiness or jiggling or something of that nature?"
"Well, as long as it doesn't overtake you when you're not trying to sleep."
Perplexed, "What do you mean?" Severus gives him an are-you-mad?! look, and reiterates, "They'll think they're penguins!" Generously, he offers, "I could make them see you as a polar bear, if you like."