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Severus frowned at the crumbling page of the old text in front of him. This was the first year he would be teaching Potions, and while he felt that he had constructed an excellent curriculum, he was already getting bored of teaching the same thing over and over.
He'd decided that the NEWT-level students could certainly handle learning a potion that wasn't in their textbook, so he'd borrowed a particularly interesting tome from Bathsheda. She'd been going on and on about the summer trip she'd taken to an incredibly tall yet seemingly unfinished tower where she'd found the text, but honestly he'd tuned out after he saw the recipe for a potion on the final page. She hadn't quite gotten around to translating it, but Severus thought that he could manage the rest with her notes, and he was sure his students would appreciate something new and fun to brew.
He was proven right on that front as soon as his students entered the dungeon and began murmuring in curiosity when he revealed the writing on the blackboard.
"What does this one do, Professor Snape?" one student asked, without raising his hand. "You haven't put a name or anything."
Severus glowered at him. "You should be able to make an educated hypothesis based on the ingredients, Mr. Havers, but if you cannot manage that, you are welcome to test the effects yourself at the end of class, assuming you brew it properly."
It wasn't often that a potion brewed in this class was safe for general consumption, so Severus' statement brought another round of excited murmurs, and the students immediately began setting up their cauldrons and copying the instructions from the board.
Severus enjoyed his NEWT class the most – these students were all here because they either enjoyed the art of Potions, or they needed it for their future career, and it meant that they were all motivated to do well. Case in point, there was little chatter, nearly all of it directly related to the potion they were brewing, and nobody needed assistance getting started. All Severus had to do was glance around the room every once in a while – or take a stroll later when the fumes got a bit thick – to ensure nothing was going drastically wrong.
By the end of class, only one potion did not look as it should, and the shade was only slightly less vibrant than the recipe called for.
"How finely did you dice your Valerian root, Havers?"
The boy in question winced. "Not finely enough?"
"Indeed," Severus said, and he took the vial with him back up to his desk to place with the other students' submissions.
"Class is dismissed once you have cleaned up your stations," he announced. "And everyone but Mr. Havers may sample their potions before they leave."
Severus seated himself behind his desk, ignoring the general chatter that sprang up, and pulled the rack of vials towards him to begin making notes in his grading ledger. Some minutes later, however, he was rudely interrupted by an abrupt rise in the noise, and a voice shouting his name very close to his ear.
"Professor Snape!" Havers cried, again.
"Five points from Hufflepuff," Severus said irritably. "Do you think I am hard of hearing?"
"Er, no sir, but it's – just listen to them!"
Severus did, and found himself absolutely shocked. The rest of the class was standing around in between their half-cleaned benches, and shouting at each other in complete gibberish.
Severus stared with a sudden feeling of horror.
"Professor? What was the potion supposed to do?"
Severus snapped back to attention. Right. He was in charge of this… disaster. Quickly, he lifted his wand, and uttered a Sonorus.
"Everyone quiet," he said, and the entire class turned to him with uncomprehending faces. "Now sit, and don't make a sound."
Almost immediately after he finished, however, his students began speaking gibberish again, turning to each other and spouting nonsense and then looking back at him again and speaking incoherently. Clearly, they did not understand what he had said, and not only that, but they also could not understand each other.
Merlin, Severus thought, what had he done? And how in the world was he going to fix it?
Wincing at another large spike in the noise level, he whipped out his wand again and gestured broadly at the room, Silencing the lot of them in an instant.
"Havers," he said, slowly and precisely, "go and fetch Professor Dumbledore. I believe his password is 'cookie crisps'."
Severus was uncertain if he'd also Silenced the Hufflepuff, or if the young man had finally learnt the value of keeping his mouth shut, because he ran off to complete his task without argument. He took a seat behind his desk and pulled out the tome he'd borrowed from Bathsheda with a sigh, ignoring the intense interest from his Silenced students, all of whom had realized the futility of trying to speak, and for the most part had decided to take their seats.
He was in the middle of re-translating the potion recipe and hoping Dumbledore wouldn't fire him on the spot when Havers returned with the Headmaster.
"Well!" Dumbledore exclaimed as he entered the dungeon. Severus looked up, sure that his fear was written all over his face.
"We are in a pickle, aren't we?"
"In a pickle?" Severus asked in disbelief. "Nearly my entire class has ingested a potion which has turned them into village idiots!"
"I wouldn't say it's as bad as all that," Dumbledore said, only slightly less jovially. "Nobody's suffered any physical injury, and we seem to have a group of remarkably self-aware village idiots on our hands. I'm sure the solution will be quite easy."
"Easy? I translated this potion from some horribly ancient runes that even Bathsheda was struggling with and then let my students brew it and sample it without having tested it myself beforehand," Severus hissed, his fear of being fired fading in the face of his anger at the harm he'd caused to students in his care. "Obviously, you should fire me."
Dumbledore merely laughed. "Don't be silly, Severus. If I fired you, who would brew the antidote?" And then, before Severus could say anything else, Dumbledore turned to the only other person in the room who could actually understand their conversation. "Come now, Mr. Havers, assist me with your classmates. Your Potions professor has some work to do."
As Severus watched in stunned bewilderment, the Headmaster managed to get the entire class to follow him with a few simple hand motions, and he was soon left with an empty room.
It took nearly a week, during which Severus berated himself constantly for his unknown error, until he and Bathsheda discovered his mistake. The ancient people who had written the recipe had not used clocks, and so Severus had quite easily misunderstood the rune which translated as 'clockwise' to mean 'counter-clockwise'. Therefore, the potion that was meant to give a person the ability to speak and understand any language had turned into one which caused a person to be unable to speak or understand any language.
Severus had never had as big a headache nor wanted more sleep than the moment when he finally delivered to the hospital wing a freshly brewed antidote to the horrible potion he had unwittingly allowed his class to ingest.
That would teach him for thinking he could be the fun Potions professor, he thought, and he resolved to never assign a fun, exciting new potion to a class ever again.