Kingsley Shacklebolt must have had a large vial of conflagration potion as he single-handedly took out an entire city block at the edge of the lake, and Cissy could only estimate a few thousand Inferi were destroyed in that one hit. That it had barely decimated the Inferi army that was slowly marching upon us... that it was only a tenth of them... This was pure extermination, and she knew her sister Bellatrix's necromancy was at work here.