She had expected that after the taunting, Bellatrix would pick up her game and dodge the attack. Instead, Hermione was mildly surprised that the curse instead hit, and the woman fell to the ground, writhing in pain and shrieking at the top of her lungs. She felt a surge of power run through her, and she was urged on by the darkness in her to continue, to torture the life out of the woman, until all she was left with was madness. She pushed harder, allowing more magic to flow through her and into the wand. She had held on so tightly to what control she did have over the darkness, but here in the midst of battle, it was unleashed.