Zombies: A Primer.

Well, with certain companies fucking around with the human genome like they are, I wouldn't doubt that a chemical outbreak will start the Zombie Apocalypse.  Someday, you'll have to make that decision to run through a crowd of smelly marauders or off yourself.  Should you decide to fight in a world where your neighbor is now trying to neatly peel your skin off and eat it, this will help you understand.

As myself and a few other discussed in Economy one day, there are 2 kinds of zombies.  Unfortunately, they may or may not be distinguishable, and one is much more difficult to kill:

VooDoo Zombies.
These zombies are not the product of any virus or chemical imbalance, these are the product of dark magic.  VooDoo Zombies close mindedly carry out the will of their summoners.  They will not stop by any means.  Despite decapitation or dismemberment, their pieces will still move, and still try to eat and kill you.  The only known way to kill a VooDoo Zombie is to somehow disintegrate the body.  Burn it, melt it, freeze it and blow it up, whatever, but NOTHING can remain.

Chemical Zombies, aka the Resident Evil Zombie.
These are the one that everyone knows and loves and the ones you probably have to worry about.  Reanimated by a virus or chemical, these guys are variable as far as how dangerous they can be.  If said walking corpse is fresh, odds are muscle memory and actually having some muscles left will allow them to literally run after you.  Depending on the lapse of time between reanimation and your encounter with them, they might be able to run, or be reduced to a slow shamble.  Pray that you can find out quickly.

9 / 10 times, the virus attacks the cells within the bite radius, eventually spreading to those within the brain, frying all higher brain function, erasing the person they used to be.  The brain is left only with basic motor movement and the instinct to feed.  Occasionally, if they're intact, sensory organs may have some slight function.  All energy in the body goes to powering what's left of the brain, and because of this, the rest of the body cannot be maintained causing Zombies to rot.  It's a vicious cycle, because in order for energy to be fed into the body, it must digest food, but how can it when the stomach is dead?  Sucks, huh?

But don't feel bad for Zombies, they don't feel pain at all.  This is their biggest asset when you're trying to stop one.  You need to aim for the head.  Destruction of the cortex is the ONLY way to ensure that this zombie you just fought off will not come back and try to take a bite out of you. Decapitation will disable the body, but the head will still try to move, unless the cortex is hurt.

You've seen it in every friggin' movie: the moment when a survivor has to kill an undead loved one.  I myself question if I'd be able to off my Mom or Dad whilst they were shambling towards me with outstretched arms, wanting to give me the deadliest snuggle hug ever.  The key to being able to do so, I would think at least, is to realize that it's not your loved one anymore.  Just some rotting husk, holding your parents soul inside.  Release them from their torment.  Save them from the wretched fate of wandering the Earth for eternity, seeking meat until they literally fall apart and die again.

I hope this helps a little!  If anything, just remember: AIM FOR THE GODDAMN HEAD! Death to the Undead!