"You probably added the porcupine quills while the cauldron was still on the fire," the nurse told Neville. "That releases the magic in the quills too quickly; it melts through the cauldron, and since you haven't added the horned slugs to neutralize the acidity, the brew hurts much more than it helps. It's an easy mistake to make. Fortunately, it's easy to fix, too—just take a properly brewed dose and you'll be fine."