After his wand fails another time, Ron slammed his textbook shut, Hermione following closely after.
"Who could it be, though?" She said, frustrated, "I have absolutely no idea— and Mayumi, stop transfiguring things into roosters!"
Mayumi spared her a glance, then pouted.
The next day, the entire castle was flooding with roosters, and Mayumi was seen being chased across the grounds by a very furious-looking Hermione.