"Who's 'He-Who-Must-Not-Be-Named'?"

"The Dark Lord who took over the Ministry, the one who started the wars. Voldemort- I guess it's safe to say his name now."

"It wasn't safe to say his name before?"

"A long time ago, it was just fear, I think, but since he came back to power, and replaced all of the disloyal Ministry workers, he instituted magic that could tell when someone said his name."

"Come again?"

"Voldemort took over the government? He used magic to track down people who said his name?"

"The government can keep track of stuff we say?"

"I don't know if they still can...the Trace can tell when you use magic outside of school, I think that's what he used." 

He makes an incoherent noise of frustration.

She pats his shoulder sympathetically.

Alistair will look vaguely sympathetic, and unambiguously confused. 

"I do not," he explains, "like the idea that the government can keep track of everything I say if they want to."

"Oh. It's not like he had anyone listening to people, just a spell that would know who said his name...and I don't think anyone would still be using it, but anyone could. You could do that to me."

"I could? How?"

"I don't know the spell. I just mean, it's not just the government that could do something like that, they just already had the Trace set up."

"Hhhgg."

"Sorry. We can probably change the law, but the magic won't stop existing."

"Yeah. I don't mind so much that it exists, actually, more that the government has it just like that."

"Oh wow, has anyone told you about the International Statute of Secrecy? I bet you'll hate that even more."

"Yes. Professor Flitwick explained it to me in very general terms, and I read all about it in the history book."

"That's what the Trace is for, and Obliviators, and...other Ministry departments and committees and things. To hide magic from Muggles."

"Obliviators?"

"If you do magic in front of Muggle, they wipe their memories. That way, no one asks the wrong questions." 

"oh."

"Don't worry, I'm sure it hasn't happened to anyone you know. Usually it's only when there are criminals, and the Ministry will send someone to explain things away first, before they send Obliviators, if things aren't too big."