Examples of Scientific Theory Cyborgian implants that send electrical impulses into muscle tissue to activate the muscles into action. This theory is easily shown with a frog's leg which is reanimated through electricity. Note that in this theory the zombies cannot spread but must be created in a lab. Biological virus infects the dead body and reanimates it while feeding off of it. The virus fixes broken down electrical receptors and allows the body to function. The virus spreads through blood and can be spread to other creatures via injuries. Nano bots reanimate the body using electrical impulses as above. The bots self replicate and anyone who comes in contact with the bots will reanimate after death. An alien forms a symbiotic relationship with a corpse and uses it for transportation. It infects other people and spreads its children in corpses it finds (or kills).

Reasoning for Reanimating Corpses: There's also the matter of why would anyone want to deliberately reanimate corpses. Religious reasons vary wildly from the urge to destroy everything to greed, hatred and revenge, but scientific reasoning is more concise and has a relatively short list. A person who has lost their spouse, child or parent attempts to bring back the dead and creates zombies instead. The military is exploring the military applications of zombies and undead troops. A pharmaceutical company seeks to reanimate corpses to learn more about saving lives, longevity, and bringing back the dead. Someone wishes to communicate with the dead in order to discover if there is an afterlife.