The Science of Zombism

Like vampires, zombies will take on the temperature of warmer environments and produce their own body heat when ambient temperatures drop between 30 and 60 Fahrenheit—although zombies are about 5 to 10 degrees warmer than vampires, with core temperatures ranging between 64 and 76 at rest and up to ten degrees higher when fully active. This physiological discrepancy is due to heat released by the various parasites living in zombic flesh—a phenomenon that causes zombies to emit steam in cool weather and phosphorescence when in water.

Zombies also tend to sweat more than vampires—due in large part to their higher temperature and poorer regulation habits—but it's mostly a case of overactive sweat glands, which are likely a physiological response to their inability to urinate. The fact that they drool profusely could be another form of fluid removal.

Another vampiric trait zombies share is the ability to survive being frozen solid, along with the act of voluntary dormancy. However, given their constant state of decay, how long they can hibernate depends greatly on the surrounding temperature: a matter of weeks in the cold; mere days in the heat.

As with vampires, zombies are sterile, impotent and presumably asexual—although bloating from decomposition can sometimes cause the genitals to appear erect. Interestingly, while vampiric testicles still retain a scarce amount of sperm (though deformed and useless), zombic testes produce none whatsoever due to higher toxin levels and poorer circulation.

The great irony of zombic life is that even as they voraciously feed, they too are being fed upon: a zombie's body is like a big Petri dish serving host to everything from bacteria and fungi to maggots and ants. The resulting state of putrefaction means, as terrifying as a zombie may be to the eye, it actually commits far worse offenses to the nose.

A long-held, common misconception is that zombies are immortal, when in actuality the vast majority of them live less than a year. It is possible to determine a zombie's age based on their external appearance—specifically, their level of decomposition, also known as necrotic degradation.

These two zombies destroyed near Gainesville, Florida in the early 1960s offer a good example of the differences between Stage II and Stage III zombies:
As with vampirism, the zombism virus has a similar effect on non-human mammals, especially other primates. Like their human counterparts, they will become aggressive, necrotic and lacking in coordination and speed—the latter being far unlike the swift zombie dogs seen in some fiction. However, as with HVV-infected animals, their symptoms are much more rabid, and as a result they don't live much longer than a few days.

Even vampires can be infected, though the transformation process takes a day or so longer due to their slower metabolism. The resulting abomination is known as a vampirozombie (or zompire), and it retains some of its vampiric characteristics, such as fangs and night vision. Everything else is rather muted: a vampirozombie will gnaw flesh as it drinks blood, it can barely feel its numbed skin burning in the sun, and its dying brain is not as prone to seizures. They are, however, still quite blinded by bright light, since their pupils remain fully dilated. Their fast-twitch muscles also make them somewhat more agile than normal zombies, but their lack of coordination prevents them from sprinting and jumping.

Interestingly, only vampires can become vampirozombies—which explains the old saying that the zombie is the last stop on the Undead Express. Even if a vampire did bite a zombie, the latter would not turn. It's not really known why, but it's speculated that zombies have far too many toxins in their bodies for the vampirism virus to function properly. As for how vampires can become infected with zombism when they're immune to most other viruses, it's believed that HZV's genetic similarities to HVV allow it easy access into vampiric cells.

Needless to say, vampirozombies were extremely rare (outside of laboratory experiments), as most vampires knew to stay well away from their undead brethren.

As for what would happen to a normal human infected with both viruses at the same time, heinous experiments performed by Nazi scientists have shown that zombification occurs in most surviving subjects, since that particular process is much more rapid than vampirism. In order for someone to become a hybrid, they first must be infected with vampirism, then zombism after they've entered the coma. What few subjects experienced immunity to one virus always succumbed to the other. Variations of these experiments included transplanting vampiric and zombic organs and limbs onto humans and vice versa—even grafting entire individuals together—with predictably disastrous results.

The preceding information brings up another question: do the vaccines work on animals and vampires? Seeing as how vaccines are basically killed or weakened virions, the answer is yes. Immune globulin, however, is a different matter entirely, since human antibodies that target the viruses are largely ineffective in other organisms. As a result, the vaccines must be administered before infection takes place. Immune globulin can be created for individual species, but the cost and manpower of such an endeavor is better spent on humans. After all, they pose the biggest danger when turned.