Though all demons feed off emotions, eaters of the dead limit themselves to a singular source: those about to perish. Whether by evolutionary development (assuming demons actually evolve) or artificial design, these beings are able to extract the fear, pain, and anger from those near to death, whether they are flesh or machine. Skilled eaters of the dead are able to keep their targets alive for extended periods of time or even to heal their injuries and diseases, as these demons have no interest in actual death.