And I thought surely they were Carrow's rats. Wasn't it obvious?

How awful one of them turned into corn.

I really hope that doesn't happen to Sebastian. It was the petrification that did it? Was it just 'petrificus totalis' or some other hex? Ugh. Maybe I should ask Professor Brutka if there's anything I can do. He seems decent, I don't think he'd tell Professor Carrow I have one of his rats.