Hermione had a cauldron that she couldn't stir without gassing themselves as Narcissa was dueling with kid gloves, merely trying to push them back. "Use Bombarda! That might actually stop them!" Thinking quickly, she pushed a stirring rod through the charm and into the cauldron, using her wand to levitate and stir the potion remotely. It took more effort than if she did it manually, but this way was safer.