Undead Sunday: Feeling safe and secure in the knowledge that zombies exist purely in the realm of fiction? Prepare to have that sense of security shattered!
Some parasites have the ability to control the animals they inhabit. This usually entails the host animal sacrificing itself in some way, as it does the parasite's evil bidding (think of them as little voodoo priests). Discover Magazine has a great article about this: Zombie Animals and the Parasites That Control Them.
Even humans aren't safe from these zombie-making parasites. There's one that is believed to cause behavioral changes, or even schizophrenia, in it's human host: toxoplasmosa gondii. Cats are the main hosts for this parasite, even though about one-third of the world's population is infected with it. It probably won't be long before it evolves into a parasite that specifically targets humans, effectively turning us all into voodoo zombies. I bet the cats will enjoy that.