Draco Malfoy and the Angel of Ravenclaw
People stuck with their housemates. They ate with them, studied with them, slept with them… socialised with them, lusted after them, slept with them. The differences between the Houses made anything else entirely too complicated.
It had to be complicated; without that, they'd all get mixed up. And people who understood things would be having none of that. It didn't seem that it mattered so much to the other Houses, but a true Slytherin knew it made no difference however beautifully bubbling a laughter the others had, or how marvellously their eyes sparkled.
But it was… bothersome, to be noticing.