Pain Is Weird. Making Bionic Arms Feel Pain Is Even Weirder

Pain is an indispensable tool for survival. The prick of a nail underfoot is a warning that protects you from a deep, dirty wound--and maybe tetanus. The sizzle of a steel skillet is a deterrent against a third-degree burn. As much as it sucks, pain, oddly enough, keeps us from hurting ourselves. It's a luxury that prosthetic users don't have.