Zombie outbreak possible?

Sure. Because, there could be something like a parasite like the Ebola Parasite that could take control of your brain, and keep all your bodily functions intact. Same with viruses. I'm too tired to explain all of it right now. Look it up on google. People who say this stuff doesn't exist are closed-minded fools who cling to whats "NORMAL" because they are programmed to, metaphorically.