Krum's face was grim with determination, his wand-tip glowing bright yellow as he used it like a dagger stabbing the corpse in the back over and over. The wand came out free in a spray of blood, but it didn't matter. The inferi by the door had reacted to pain, but once they started killing or... feeding, they were just reanimated corpses following orders. You couldn't hurt the dead, and you sure as hell couldn't kill it.