If a zombie was real how would it live?

how would a zombie live if it's dead i know they are called the undead cause i read the zombie survival guide and looked up on the internet how some zombies live but then the virus isn't real and then nano bots in the body causing the body to reanimate and be a zombie.But wouldn't the body need to be alive to become reanimated into a zombie.I know this may sound confusing to you but all i'm sayin is how will it live,and when the person is dead wouldn't they remove the nano bots anyway?