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Zombies are present in the folklore of Haiti, where they are created by Voodoo, which is an African type of Black Witchcraft.

More recently, zombie films have exposed new theories according to which man-made virus or genetical experiments are held responsible for the creation of zombies.  Such films put a strong emphasis on flesh and blood, rotting bodies and their attendant maggots, as well as the still-warm gore resulting from savage often cannibalistic attacks upon the living.

Zombies have been confused with many other monstrous creatures.
Some zombies have the appearance of the living, but their lack of free will and souls give them the appearance of mechanical robots.  Others display visible signs of decay and emaciation on their face and body. They have blank expressionless faces that become more animated when they get hungry and engage in a feeding frenzy.
Zombies are grey, move very slowly and change direction randomly and frequently unless they can see something moving in front of them, in which case, they start walking towards it.  After a while they get bored and wander randomly again.  They are near-mindless, possessing little reasoning power, though many can perform "remembered behaviors" from their mortal existence.  They are incapable of speech, but often tend to make moaning sounds.  They are normally encountered wearing whatever clothing they wore in their human life, prior to reanimation.
The idea of a rotting corpse brought back to life possibly has more to do with the work of novels and movies. 

However, the idea of zombies as drugged individuals, pronounced dead and then buried alive in a coffin awaiting complete brainwashing appears to hold more truth.
Some of you might wonder exactly what classifies something as a zombie.
Well, people's opinions vary, but the most common consensus is that a zombie is any re-animated corpse. 

You can take this a bit further and say that any re-animated once-dead body part is considered (a) zombie.
Most people doubt that zombies could exist in the actual world.

In philosophical terms, they are naturally impossible.

But many people think that they are at least logically possible!