"Are you really?" said Hermione. "I know all about you, of course — I got a few extra books for background reading, and you're in Modern Magical History and The Rise and Fall of the Dark Arts and Great Wizarding Events of the Twentieth Century."
"Oh, what do they say?" Harry asked, faking interest.
Words began to splatter out of Hermione's mouth. "Well, they talk a bit about the war, what was happening, and so on. And about you they don't say too much, but that You-know-who apparently wanted to -" she paused, and continued in a quieter voice "- kill you. He killed your parents, and then he cast the Killing Curse at you, and apparently, you survived. No one survived it before."
"Well, it can't be really true, can it?", Harry asked, his tone condescending. "Nobody knows, because nobody was there that night, besides my parents, Voldemort and me. Three of them are dead, and I know wasn't asked. Perhaps your books aren't always right, you know?" He paused, looking up and down at Hermione. "God, you're such a stupid know-it-all."
At that point, Hermione looked ready to cry. But before she even had a chance to start, an older student entered the compartment. His was muscular, wore a blue tie, and on his chest was a golden badge with the inscription "Head Boy".
"I'm sorry, I couldn't help to overhear… Are you saying that no one could really know what happened the night when You-Know-Who died, because no one was there ?"
"Yes. I mean, how could they?" Harry answered. "This whole society is stupid! Nobody questions the lies they feed them! Sheeple!"
The head boy slowly shook his head and closed the door behind him. With deliberate movements, he took out his wand and waved it around, silently muttering strange sounding words.
"Okay, I know the following: You," he said, pointing at Harry, "opened a chocolate frog card, and … it jumped out of the window? Interesting."
The head boy turned and looked at Ron. "I will assume that you are a Weasley, and have tried a spell of the twins." He waved his wand a bit more. "'Turn this stupid, fat rat yellow?' - how could you believe this was a real spell?"
Ron blushed and mumbled something inaudible.
The head boy waved his wand a bit more, all three first-years looking at him. He stopped when the tip of his wand glowed blue for a moment. "That's all I got."
He turned to Harry again. "I hope you see now that detecting that a freaking Killing Curse might not be too hard, especially for someone like, you know, Dumbledore ."
The head boy looked down at Harry. "Remember, all magic leaves traces."