We found out recently that if you try to leave a little kid in a graveyard late at night, he'll freak out. Even if you offer to leave him a gun to protect himself. Why? It's because on some instinctual level, all humans know it's just a matter of time until the zombies show up.
Our culture is full of tales of the undead walking the Earth, from our religions to our comic books. But, some sort of zombie apocalypse isn't actually possible, right?
Actually, yes. It's quite possible. Here's five ways it could happen, according to science.