Neville was casting knockback jinxes at the thing's head so hard that his arm was getting tired as if he were a beater in Quidditch. The corpse's head was bleeding, cracking, but it wasn't letting go. Its head was buried into his chest like a monstrous child, feeding. Inferi aren't supposed to want to eat, only shamble around and sometimes take a swing at you. The Goblins raised them as bloodthirty and hungry as they were.