His thigh is burnt. So badly, to her eyes at least. Edging toward third degree burns, but from his reaction, not badly burnt enough to kill the nerve endings, or he wouldn't be making those breathy, choking screams, or sobbing so hard. Hermione supposes that's probably a good thing, compared to the alternative of even more serious burns. It doesn't feel like a good thing. Although at this point she thinks she mostly feels numb inside, overloaded and burnt out by the horror. Her knee is searing, and if one little burn feels this bad, then how does Malfoy feel? This is worse than anything that he has ever done to her, and she hates her helplessness, she hates that she is doing this.