While this is the fastest way to put them down, it is not the only method of killing them. They only appear to be impervious to other methods because of the overflow of adrenaline caused by an altered brain. While they can be put down with stabs and shots to the chest, they have the ability to withstand an incredible amount of punishment. Also Attacks to the head area saves ammo consumption which is critical to survival when forced to confront either a group, or a single infected individual.