"You, over there." Snape directed the Potions Club students to form a circle in the greenhouse. "Set it up the way I just taught you."
The students raised their wands, aimed them at a cube, and levitated it.
Before long, the cube "melted," forming something like an umbrella stand. When it landed on the ground, the "umbrella frame" spread flat against the floor into a circle, finally forming a protective spell resembling hexagonal polarization.
"With this, at least you won't have to worry about burning down the entire greenhouse," Snape said acidly.
At that moment, no one cared how unpleasant he sounded. They were all delighted with their "work."
The Potions classroom had been placed in the dungeons not merely because they were suitably gloomy. When Salazar Slytherin designed them, he had already anticipated that many wizards would oppose him in the future. Thus, he had not only built the dungeons solidly, but also laid down numerous reinforcing spells.
Yet the dungeons had never truly been used as dungeons. The spells meant to prevent prisoners from escaping had become protective magic. Even if someone really turned a potion into explosives and caused an explosion, it would not affect the rest of the castle.
Sunlight reacted with many substances. Like faded murals, their pigments oxidized under the sun. But Pomona would never agree to turn the greenhouse into a cellar. The plants inside needed sunlight, even though night had already fallen.
"Stop standing around together. The castle will be closing soon," Snape threatened. "If you break school rules, don't expect me to plead for you."
"No one was expecting that," someone said from the crowd.
"You could spend your time packing up your things instead of nagging like an old woman, Mr. Caldwell," Snape said, his back to the student complaining