Bella and Harry were flinging curses back and forth madly, and Hermione decided then and there that they had to start using spells stronger than expelliarmus and stupefy. Voldemort’s right-hand woman was using two of the Unforgivables and any number of dark spells that were designed purely to maim and rend flesh and psyche. Harry wasn’t going to be able to sustain the frenetic level of duelling Bellatrix was engaging in for very much longer if he kept only using defensive or immobilising spells. If he got a hit in Bellatrix would be stunned or wandless – if she hit Harry, however, he’d be dead or in an enormous amount of pain.