All characters, this world, and Snape's speech belong solely to JK Rowling
Harry sat quietly in his seat, nervously anticipating his first-ever potions class. He drummed his fingers on the table, gazing at the chatting students around him. He was seated next to Ron, who was bemoaning not having finished his breakfast that morning. "I didn't even finish my toast!" he practically wailed, and Hermione glared at him, hissing, "Honestly, Ronald, it's your own fault for sleeping so late! Now pay attention!" She turned back around, staring pointedly at the board, while Ron angrily muttered, "The git isn't even here yet. There's nothing to pay attention to!"
Harry sighed. He didn't particularly like the over-bearing girl either, but Ron couldn't seem to leave her alone. And she did make a good point; Ron had overslept for the third time that week, and had nearly been late to class. As a matter of fact, Ron really wasn't the best of friends he could have made; however, as his first friend, Harry felt it wrong to just ditch him. None of his classmates were particularly interesting to Harry, most of them being very loud and overbearing. He wondered, not for the first time this year, whether the house of the brave was best for him.
Turning his thoughts back to the class, Harry began fiddling with his quill, stroking the feather and tapping it on the desk. He had been interested when he read the first chapter of his potions text, but wasn't so sure about the professor. Professor Snape had given Harry a distinct feeling of discomfort, glaring at him during the welcoming feast. His dark eyes and stiff stature certainly made his name fitting, and Harry hoped fervently that he wasn't too hard on him today. 'Probably ask me all sorts of difficult questions,' Harry thought solemnly, 'I'm glad I read the text.'
Suddenly, the door to the classroom burst open, admitting the man in question. His dark robes swirled about him, curling lightly around his feet as he swept to the front of the room. Harry admired the way they seemed to ebb and flow, even as the professor came to a stiff halt and spun about, eyes seeking out each of the students. His gaze locked on Harry's for a split second before the professor began to speak in an eerily calm sort of voice that was barely above a whisper.
"You are here to learn the subtle science and exact art of potion-making," he began. "As there is little foolish wand-waving here, many of you will hardly believe this is magic. I don't expect you will really understand the beauty of the softly simmering cauldron with its shimmering fumes, the delicate power of liquids that creep through human veins, bewitching the mind, ensnaring the senses...I can teach you how to bottle fame, brew glory, even stopper death—if you aren't as big a bunch of dunderheads as I usually have to teach."
The class was dead silent. No one moved a muscle as Professor Snape stared steadily out at them, until Snape barked, "Potter! What would I get if I added powdered root of asphodel to an infusion of wormwood?"
Harry gulped nervously. He was sure that he knew the answer, but his overwhelming stupidity overcame him and he burst out with, "If I answer your question, Sir, will you answer one of mine?"
Harry almost clapped a hand over his mouth in horror, until he saw a glint of humor flit through Snape's fathomless eyes. He fearfully awaited his punishment, for certainly his cheek would get him in trouble? But Snape merely said, "Why, Potter, spoken like a true…Slytherin. Quite unexpected. Why don't you answer mine first, and we'll see?"
Harry stared at his teacher in shock. He thought that he would be eviscerated, but Snape seemed to be humoring him. He decided that he had better answer the question before Snape changed his mind.
"A very powerful sleeping potion called the Draught of the Living Death, Sir." Harry said confidently. "Will you tell me what I wish to know?"
Snape's lip twitched, as though he thought this slightly amusing. "Yes, Potter, if I agree with the question."
Harry thought a moment. "Sir, why do people dislike Slytherins?" Harry asked, leaning back on his stool a bit.
Professor Snape eyed Harry warily, warningly, as he carefully said, "A simple misconception. Many believe that all Slytherins must be dark, or evil, right from the moment they come into this world. However, Slytherin house, while having a great deal of very powerful people, is also a house that combines many traits of very successful people. How would the Minister get where he was without ambition? He needs to have a goal, a plan, and the drive to achieve that plan. A very Slytherin quality, but not regarded as a bad thing when it works in favor of the whole. It matters not how powerful a Slytherin is, when he has the cunning to outwit his opponent, with the instinct of when to back down. All Slytherins are loyal to themselves. This is one of the reasons that Slytherin House is often equated with dark wizards; because dark wizards must be cunning, and ambitious, but do not need wisdom, bravery, or loyalty. However, this does not make all Slytherins dark. Does that answer your question, Mr. Potter?"
"Yes sir. Have you any others for me?"
"Yes, actually. Why the interest in Slytherin House all of a sudden?"
"Question for a question, Professor. Why are there so many misconceptions about Slytherin?"
Snape eyed him, considering. He leaned back against his desk and began tracing his mouth with his index finger. "I suppose it started all the way back to the founding of the school. Salazar Slytherin, founder of Slytherin house, was against accepting muggleborn children to the school, because he feared magic being discovered because of the student's muggle relatives. Muggles tended to go for the torch-and-pitchfork approach to witchcraft back then, and protection of the school was his priority then. This was the beginning of people mistakenly thinking that Slytherin believed in purity of blood as an indicator of magical power. Of course, later on, Slytherin House's image wasn't helped by the fact that the Dark Lord himself was a Slytherin, as were many of his followers. However, during the first war, he had followers from every house, including Gryffindor. Make no mistake on that."
"Yes sir. And your question?" Harry was very pleased with how this conversation had turned out. He was considering getting to know some of the Slytherin students, as they seemed much quieter than his own house mates.
"Ah, yes. Why your sudden interest in Slytherin house?"
"Well, Professor, it seems I may have made a mistake at my sorting."
"Oh? And how did you come upon that conclusion?"
"The hat said I should be a Slytherin. I'm starting to believe it was correct."