From a biological point of view, when can a human be considered dead? after brain activity ceases? after the heart stops? after all human cells cease metabolic function? If a human brain were to cease functioning, but the body is kept going on a life support macine, with all basic functions still working, can it be considered alive (compare to a headless chicken)? Can a person be considered dead if a doctor could still revive them through whatever means? any thoughts?