"They could give you separate detentions," Miranda points out, "as the entire point of the exercise is to be unpleasant."
"Well, I suppose they could tell Sally not to visit me during detention. It would be difficult, though. Considering that we have two-way mirrors. And backup devices of that nature. Specifically designed to prevent that sort of thing."
"I'm not a teacher or anything, I'd just be careful if I were you," says Miranda.
"I will. Probably. But I'm still going to beat the shit out of anyone who says or does anything unpleasant to Sally."
"...I mean, it's not like I'm going to hit you. You seem very unlikely to say hitworthy things, as a person. Also we're friends?"
"Well, I might be unlikely to say hitworthy things, but I don't know exactly how unpleasant I would have to accidentally or incidentally be to Sally before you would decide to hit me for it, so if I care a lot about not being hit, and I kind of do, do you suppose it is really safe to be her friend, and is that something you want anyone to be thinking on the first day of school?"
"It's not- it would- this is a bullying thing. Not- Unpleasantness is- deliberate. You're not that. It's- 'hey, m- mudblood!' Or. Whatever- stuff, like that. You don't- you're not that kind of person."
(Ari seems to be pouting somewhat. He hits people for justice.)
"Well, the warning you gave me wasn't very clear until after this had already occurred to me," Miranda says.
"It wasn't a warning. That'd be like warning someone that you'll be upset if they throw your sister off a cliff. It was pretty much conversational."
"Still, I'd recommend being more specific if you need to notify anybody about your - inclination, here. Otherwise it just sounds like you're threatening to hit children smaller than you if they interact with your friend and make a wrong move."
"Neither of us has a lot of experience here," Ari notes.
"I mean, you'll notice that I didn't get up and leave the compartment," Miranda says. "But it didn't sound good."
"That would have been unpleasant. I'm glad we didn't make you run away."
Ari re-dedicates his attention to the unfortunate bird, which has backslid into a breccia'd sort of texture. He mutters unpleasantness before resuming nonverbal wandwork.
Ooh, a snacks trolley. Miranda buys a pack of Chocolate Frogs.
Sally buys herself a Peppermint Toad and Ari an Acid Pop. He takes it appreciatively. An unpleasant hissing and bubbling sound comes from his mouth; he doesn't seem to mind.
Meanwhile, elsewhere on the train, a girl is alone in a compartment putting Spellotaped-ended bits of paper into her Potions reference to clearly mark the locations of key items.
"Um. We've met, I think. Our parents know each other. Can I sit here? You seem like you won't hex me."
"I won't hex you," giggles the girl. "You're one of the... Santana Vega...? kids."
He slides into the opposite seat. "At least one, yeah. We can't really keep track either."