#5. Brain Parasites
Parasites that turn victims into mindless, zombie-like slaves are fairly common in nature. There's one called toxoplasmosa gondii that seems to devote its entire existence to being terrifying.
This bug infects rats, but can only breed inside the intestines of a cat. The parasite knows it needs to get the rat inside the cat (yes, I realize this sounds like the beginning of the weirdest Dr. Seuss poem ever) so the parasite takes over the rat's brain, and intentionally makes it scurry toward where the cats hang out. The rat is being programmed to get itself eaten, and it doesn't even know.
There are certain kinds of poisons that slow your bodily functions to the point that you'll be considered dead, even to a doctor (okay, maybe not to a good doctor). The poison from fugu (Japanese blowfish) can do this.
The victims can then be brought back under the effects of a drug like datura stramonium (or other chemicals called alkaloids) that leave them in a trance-like state with no memory, but still able to perform simple tasks like eating, sleeping, moaning and shambling around with their arms outstretched.
#3. The Real Rage Virus
In the movie, it was a virus that turned human beings into mindless killing machines. In real life, we have a series of brain disorders that do the same thing. They were never contagious, of course. Then, Mad Cow Disease came along. It attacks the cow's spinal cord and brain, turning it into a stumbling, mindless attack cow.
You know all that controversy out there about stem cell research? Well, the whole thing with stem cells is that they can basically be used to re-generate dead cells. Particularly of interest to zombologists is neurogenesis, the method by which they can re-grow dead brain tisssue.
Nanobots are a technology that science apparently engineered to make you terrified of the future. We're talking about microscopic, self-replicating robots that can invisbily build--or destroy--anything. Vast sums of money are being poured into nanotechnology. Sure, at some level scientists know nanobots will destroy mankind. They just can't resist seeing how it happens.
Scientists have already created a nano-cyborg, by fusing a tiny silicone chip to a virus. The first thing they found out is these cyborgs can still operate for up to a month after the death of the host. Notice how nano scientists went right for zombification, even at this early stage. They know where the horror is.
According to studies, within a decade they'll have nanobots that can crawl inside your brain and set up neural connections to replace damaged ones. That's right. the nanobots will be able to rewire your thoughts.