Hermione blushed, before looking up at his scrutinizing stare. "I got some extra potion books and learned about what each ingredient does, and why it is added to what potion. After that, I went with my logic. Instead of adding two horned slugs I added three, because that makes the potion more potent. It would explode if I added the porcupine quills after, but to balance the slugs out, I added knotgrass, which is known to balance out potions."