Originally posted on AO3 July 2020, where there is no existing tag for original snake character
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It started with Snape, unfortunately. With a fifteen year ambition his at last, he flouted his authority in newly antagonizing ways. Harry had not mastered nonverbal casting before the curriculum moved on, but Snape had stopped making an example of him after realizing Harry was ready to knock him over at the drop of a hat. Within two weeks, though, Snape had invented a new ritual by demanding that Neville spar with someone to demonstrate the day's topic.
"Potter," he called reprovingly, "since your reflexes are so dependably destructive, I am certain you will not be harmed personally."
Harry stood up without saying anything. He'd spent plenty of time sparing with Neville, but took no joy in being part of whatever public cruelty Snape had planned. He stood opposite Neville at the front of the room.
"To ensure the odds are fair, Potter will be demonstrating nonverbal casting as he employs his defense."
Neville's face contorted with fear and Harry grit his teeth to smile reassuringly at him. He started to concentrate on a stream of protego, protego, protego. . .
"Repeat the curse after me, Longbottom."
Neville repeated it twice to no effect. On the third cast, Harry's face erupted with something rough and spiked. It was large enough that he could see it growing.
With a look of horror, Neville jabbed his wand forward and exclaimed "Finite!"
Harry's facial growth faded to normal in an instant. He hadn't realized it had blocked his windpipe until he was breathing again, bent over his knees. Snape glared at them and spoke quickly.
"Longbottom, what did I ask you to demonstrate?"
Neville barely managed to look at Snape without flinching. "The horn tongue hex."
"Did I ask you to use any counter-curse we had not covered?"
"N-no."
"Since you are so eager to move the curriculum forward, can you outline for the class the effects and advantages of this incantation?"
Neville looked like a deer in headlights. "Er," he said very slowly, "it removes. . .some curses. Not. . .everything. . .but more than. . .specific. . .counter-curses."
Snape curled his lip. "Quite."
There was cruel laughter. Even Seamus Finnigan laughed nervously, at great betrayal to his house. Snape surveyed the room imperiously.
"The true incantation is 'Finite Incantatem.'
"It is not merely a counter curse. It creates the invaluable spell canceling effect. Within a great area, it disables all minor hexes, charms, and even some enchantments. Truly devastating magic is unlikely to be affected, though that will depend on the abilities of the user, as does the precise distance covered. As one can imagine, it does not require targeting, nor knowledge of what affliction or benefit is being provided.
"What Longbottom demonstrated was a crude portion of the full effect. You will not reach the same potential without finishing the spell. Question?"
Seamus had raised his hand. "But you can cancel one spell, at least, just by saying half of it?"
"It is not the intended purpose."
"But it is faster to say."
"Yes, Finnigan, it requires two fewer seconds to speak."
"So if you're in the middle of a duel, it could still be useful?" asked Malfoy without raising his hand. It could only be a sign of real anger, Harry thought, that Snape criticized a response from Malfoy.
"Any time used to turn one's wand on oneself while facing an imminent opponent," Snape drawled, scowling even as he patrolled the room with leisurely command, "is a missed opportunity to disable one's opponent and an open window for them to disable you. Unless your strategy involves providing assistance to a wizard that is assailing you, I do not advise committing the half incantation to memory."
The Slytherins around Malfoy snickered and Neville's face burned.
"How come we didn't learn spell canceling right off the bat if it's so useful?" Ron wondered when they were packing up to leave.
"Well it is a bit tricky for a start. They don't list it in Basic Curses and Counter Curses. Snape said it's ahead of the curriculum because it really is NEWT level," Hermione said.
"How's Neville casting it then?" Ron paused. "No, y'know what, forget I asked. He's had plenty of opportunity for practice."
"It's funny, though. I don't think I've read about half the incantation working. . ."
Harry was certain Neville hadn't been using it last year. Wherever he'd picked it up, he was still rapidly improving, then. Like in the DA. . . But the thought of the DA made the lingering experience of Snape's defense class that much worse.
He saw Neville ducking out the door and lied quickly. "I wanted to get to the bathroom, could you guys go on ahead?"
He made it away fast enough to avoid Ron joining him and waited until Neville had gotten into the crowd of students before making an ambush. He greeted Neville loudly and dived in.
"Nice counter-curse."
"Oh, yeah," he replied, looking Harry up and down like he expected someone to jump out from behind him. "I guess it'll be more useful after a fight."
"Where'd you see that one?"
Neville seemed surprised. "Lupin showed it to me."
"Lupin?! When?" Neville wasn't supposed to know about the Order, when had he-
"At the ministry. You forgot?"
Harry stared at him blankly.
"You were right there," Neville explained. They were standing still and sharing intense confusion now. Harry wondered if he just had trouble remembering all the distressing situations he got into.
"Oh. Well." He changed the topic to preserve his sanity. "Y'know, you've hexed me plenty of times for practice. You must be used to it."
"That doesn't mean I like it," Neville said, abashed. "That one was nasty. When d'you think we're gonna get to the stuff that's too dangerous to demonstrate?"
"What makes you think he won't make us demonstrate those?"
"Please don't say that. . . "
/
Three weeks into the semester, Snape crossed a line. Dispensing with the illusion of fairness, he had allowed several Slytherins to help him "demonstrate" the weaknesses of the shield charm by casting at Neville from multiple sides. The fact that Neville had the ability to remove anything they cast on him was countered by the fact that they didn't give him time to do so, and occasionally silenced him so that he could "practice" silent casting. He had so far not managed it once. If Snape kept his word, he would be continuing this for another three variants on the shield charm that even the DA hadn't covered.
When Harry tried to talk to him in a free period, Neville knocked him in the shoulder and blew past without speaking. Harry was left in standing alone in shock.
His mood was fouler than ever by lunch. "This is exactly why Snape should never have got the job. At least when he was doing Potions he wasn't allowed to hex anyone."
"Don't envy anyone who gets on his bad side now. Should we do something?" Ron suggested.
"I already asked him and he says he doesn't want help," exclaimed Hermione. "I don't know what's got into him! I said we should go to McGonagall and he looked at me like I had gone mad!"
Harry understood him a bit. "What exactly would she do?"
"She'd make him stop."
"He's allowed to hex us, every Defence teacher we've had was. Snape'll ignore her or get worse," pointed out Ron.
"It wouldn't be the first time," Harry said darkly.
"By the end of the year he'll be using the Imperius curse like Moody, right? Because it's part of the 'curriculum.' Nothing we can do about that," Ron said, looking for all the world like he'd eaten something sour.
/
Harry was out of his mind that he couldn't do anything about Malfoy's obviously nefarious behavior. The least he could do with himself was ruin Snape's life.
Neville was getting more difficult to catch than he had been first year, and Harry practically had to chase him after finding him outside the Great Hall after dinner. Luckily he had experience in circular arguments lately.
"Hermione said you blew her off, too," he said, raising his voice in the most commanding way he could.
"Hermione's in a dozen NEWT classes, she doesn't have time to worry about me," he told Harry with no shortage of annoyance. "Besides, Snape's punished her for helping me, and I don't want anyone to walk in on us practicing. If Malfoy or any of his group see they'll use it as an excuse to say they were helping me practice themselves."
"I'll get McGonagall to lend us her room," Harry said as quickly as he was walking to keep up with Neville's short legged half-jog, "she did before. I won't tell Hermione or anyone, no one's going to walk in on us and you won't have to have anyone watching you."
"You've got quidditch." Neville was shrinking into himself as they argued.
"Not all year, not all the time. C'mon, Ginny and Luna are in their OWL year, I bet they don't have as much free time as I do. I know you're practicing alone, just let me help."
Neville rounded on him.
"Are you going to let up?"
"No, I'm going to chase you around the castle until you say yes," he said matter of factly, careful not to glare when Neville was already worked up. "I might start practice now by hexing you."
"I can just practice more with Ginny or Seamus then. . ."
"You can do that too. We can do more and work ahead. That'll really piss Snape off."
This idea didn't fly the way he'd hoped. "You want to make him worse?"
"He doesn't have a comeback for everything! Look, I don't think we can make him stop being-himself. But we can take him down a notch together. Wouldn't you like to wipe that smirk off his face?"
Neville was being very wary of him. "I don't want to be part of you. . .smart mouthing him."
"But the part where you hex him back?"
Neville wavered. "Fine."
/
Harry ended the next day's classes ecstatic. At bare minimum, it would be fun to practice his favorite subject without Snape there to ruin it. At best, Neville would knock Snape across the room with a silently rebounded curse that he couldn't be punished for, and Dumbledore would announce that their professor had been so grievously injured the school would be temporarily reinstating Lupin as a substitute. Snape would only come back at the end of the year, just in time to get fired or killed like every other DADA teacher they'd had. There were no downsides.
While dreamily considering which curse Snape would be inflicting on himself in this scenario, he entered McGonagall's office. She was immediately amicable to Harry's request.
"I suppose I should expect Miss Granger and Mr Weasley as well? Hopefully not too many more." Harry expected she was pretty relieved the school was running out of Weasleys.
"Just me and Neville, actually," Harry clarified. "We thought we'd work ahead. Keeping up with a NEWT level course, you know."
McGonagall was temporarily speechless. To his horror, she appraised him with a glowing look. "I see. I hope his studies go well."
Harry shifted uncomfortably. Part of him wanted to say it wasn't what she thought, but explaining that Neville was a fairly average student for the class who was joining in on Harry's rivalries seemed lousy. He wanted to leave the room, fast. "Right, yeah. Thanks again professor." He went for the door making as little eye contact as possible.