While bookshelves and video aisles are full of stories based on the mythology of vampires, comparatively little folklore exists that is unique to zombies, since they share quite a few characteristics with their vampiric cousins. Many zombie myths arose out of African and Caribbean superstition—a fact not surprising when one considers the disproportionate number of zombies in tropical regions.
Zombies are reanimated corpses
Night of the Living Dead (1968)
Source: A zombie's decaying flesh, catatonia, cold temperature, black blood, reduced bleeding and lack of a heartbeat, along with observations of apparently-dead bite victims rising again as zombies. This myth has also been applied to vampires for many of the same reasons.
Fact: Despite appearances to the contrary, a person infected with the zombism virus never actually dies before awakening as a zombie. For instance, zombic circulation is taken up by the skeletal muscles, rendering the heart inert.
Zombies are immortal
Source: As with vampires, zombies are highly resistant to injury, along with the fact that turned victims arise from comas—an event often misinterpreted as some sort of resurrection.
Fact: Most zombies live less than a year. Even if they manage to remain fed and avoid extermination, they will eventually either starve to death as their GI tract becomes too necrotic to absorb nutrients, or die from respiratory failure. While vampires often fare better than zombies due to their speed, intellect and agelessness, they too are far from immortal.
Zombies are created by voodoo spells
I Walked with a Zombie (1943)
Source: West African and Caribbean slave mythology, along with the large numbers of zombies in tropical areas.
Fact: Like their vampiric cousins, zombies are created by the transmission of a virus.
Zombies are brain eaters
Fact: Well-fed zombies can afford to be discriminating, as they will generally eat the more nutritious brains and bone marrow and leave the rest of the corpse untouched. However, hungry zombies will leave only the bones. On a related note: as touched upon in Return of the Living Dead, zombies do in fact experience chronic pain, and the various neurotransmitters found in human brains and bone marrow provide them temporary relief. Unlike that movie, however, zombies are unable to speak.
Zombies can be created by exposure to toxic chemicals or radiation
Tarman from Return of the Living Dead
Source: Innumerable B movie plotlines, which likely came about due to the fact that exposure to such elements can cause the skin to slough off, much like a zombie's.
Fact: While toxic chemicals and radiation are quite effective at cooking flesh and causing cancer, sterility and birth defects, they absolutely cannot create zombies. In high enough doses, it's even lethal to them.
Zombies lack blood circulation and do not need to breathe or eat
Mitochondria require oxygen and glucose to produce long-term cellular energy.
Source: Association of zombies with corpses.
Fact: Although slowed to minimal levels, zombies do in fact require all of the above in order to create enough adenosine triphosphate (ATP) for long-term muscle movement and brain function. If zombies had to rely on anaerobic respiration and autodigestion, they wouldn't last very long at all, and would be far too weak to pose much of a threat. Furthermore, if they had zero circulation, all the blood would pool into the hands and feet, causing them to swell and necrotize faster, rendering the zombie even more immobile and unable to hunt.
Zombies have no physical sensations & are unaware of other zombies
Source:The Zombie Survival Guide by Max Brooks (son of famous filmmaker Mel Brooks). Published in 2003, the book basically attempts to explain zombies as they appear in George Romero's movies, while readily admitting that their assumed biology makes very little sense and seemingly violates every natural law—requiring no rest or fuel and being borderline invincible against everything except brain damage. Still, this doesn't stop the author from ironically lambasting Hollywood zombies as being "fantastical and unrealistic."
Fact: If the former claim were true, zombies wouldn't even be able to stand—let alone walk and capture prey. As for the latter, zombies are actually surprisingly social creatures, being able to communicate with one another using grunts and gestures, much like apes. Also included in the book is the disproven myth that humans use less than 10 percent of their brain capacity, in an attempt to explain how zombies could locate prey without their other senses (which isn't true, either). On a closing note, there is no such thing as a zombism virus called Solanum, which is actually a genus of flowering plants. And while it's true that the (real) zombism virus is ultimately fatal to non-human mammals, it has no effect whatsoever on non-mammals—contrary to the book's claim that it somehow kills and repels all forms of wildlife.
Firearms alert nearby zombies
Source: True under certain circumstances.
Fact: Not only do zombies lose all of their hearing within a couple months, their powerful sense of smell allows them to sniff out prey within a mile-wide radius. As a result, unless you're able to mask your scent, it doesn't really matter how quiet you are.
It takes only one headshot to kill a zombie
Source: Likely from layman observation of expert marksmen who knew where to shoot. Possibly confused with vampires, whose brains are much more vulnerable to injury.
The Walking Dead
Fact: Unless the brainstem is hit, zombies can survive multiple gunshots to the head and keep coming—though not without some reduced functionality in sensory and movement. Essentially, you need to remove a zombie's head from its body to stop it, preferably with a shotgun (or a sword). Using anything else requires more precision, such as a pistol in the mouth or a sniper round through the base of the skull. Automatic weapons tend to be rather wasteful, and are better suited for vampires anyway. Lastly, unless poison or fire is added to each bolt, crossbows are practically useless against either species.
Severed zombie heads can survive without a body
A severed zombie head being "put down"
Source: Observation of zombie heads continuing to blink and bite.
Fact: While it's true that zombie heads can remain conscious for up to a minute after decapitation, any movement after that is purely reflex action.
Older zombies can learn new information and become smarter
Bub the zombie from Day of the Dead
Source: George Romero's movies Day of the Dead and Land of the Dead.
Fact: Although true for early-stagers, zombies ultimately become less intelligent as they decay and lose brain function.
Zombies never sleep
Source: Observation of waking zombies possibly mistaken as corpse reanimation.
Fact: Zombies do in fact sleep, if only for a couple hours at a time. A long string of catnaps is probably the best way to describe their sleep cycle.
Zombies become docile & can be used as camouflage when their jaw and hands are removed
Michonne and her "pets"
Source: AMC's The Walking Dead.
Fact: "Disarmed" zombies, overwhelmed with panic and confusion, will actually thrash around violently until they pass out from exhaustion, sleep for a while, then wake up and repeat this cycle until they die of starvation. Even if that weren't the case, zombies operate mostly on scent to distinguish prey from themselves, and it takes a lot more than being near a zombie to mask it. Which brings us to our next entry:
Humans can mask their scent to keep zombies from attacking them
The latest fashion of the modern zombie hunter?
Source: Recent breakthroughs in zombic research.
Fact: Experimental "deadsuits" employ the suppression and filtration systems of the modern wetsuit to mask the human pheromone, while the addition of several non-toxic plant extracts used to simulate the scent of rotting flesh transforms the wearer into a "zombie." These have functioned wonderfully in the field, with the only real drawbacks being heat discomfort from the suit's insulation and breathing difficulty in the respirator equipment. Maximum time in the deadsuit is about 3 hours.
Orgone-charged water can ward off zombies and even destroy them
An orgonite pyramid
Source: Orgone energy is a hypothetical universal life force originally proposed in the 1930s by Wilhelm Reich, and the term itself is derived from the word orgasm. Said to repel negative and malevolent forces such as demons and other evil entities, it's basically just a New Age incarnation of garlic and holy water.
Fact: Unless you drown them in it, orgone water has absolutely no effect on zombies or vampires. As for orgonite itself: while aesthetically pleasing, you'd be better off using it as a paperweight.
Zombism outbreaks can last for years & spread across the globe
Source: Numerous zombie films, which tend to rely on the myth that zombies can function for years without eating or sleeping.
Fact: Because zombies travel slowly between towns and cities and break down quickly without food, most outbreaks are strictly local and last only a week or two at most. Furthermore, the virus isn't airborne and takes at least 8 to 14 hours to create a zombie; and ingesting contaminated water rarely results in infection. Mosquitoes pose some airborne danger, but the virus usually dies in their system between meals. Considering that transportation of infected rats is the most efficient means of spreading the virus, it would take considerable human effort to cause even a statewide epidemic.
Zombies can only be killed by dismembering and burning them
Zombic remains being burned
Source: Exaggeration of zombic dexterity, along with the burning of their corpses to prevent further infection. This myth has also been applied to vampires for the same reasons. Specifically, because they were thought of as reanimated corpses, it was assumed that every body part could function and move on its own—a myth reinforced by the fact that severed zombie hands can reflexively move their fingers.
Fact: While dismemberment and incineration are effective methods of extermination and disposal, they are by no means the only ones.
Zombies retain memories and are capable of revenge
The meaning of the term undead
Coined by Bram Stoker, this term is generally used to describe a reanimated corpse in its most literal sense. Still, it was eventually adopted by the scientific community to describe both vampires and zombies, which are very much alive but simply give the appearance of being dead—their corpse-like coma and body temperature, slow circulation, dark blood, cardiac arrest, etc. Unfortunately, it still creates a fair amount of confusion among those who are ignorant of vampiric and zombic biology, or how the human body works and what can and can't be changed about it. For example, it tends to be treated as outright blasphemy to suggest that a vampire or zombie needs to breathe, or move their bowels.
Robert Lomax's explanation for AMC's The Walking Dead
The most plausible scenario (in my humble opinion) is a hypothetical species of parasitic nanotubes, which are spread mainly through inhaled spores—hence why everyone is infected. From there the parasite grows throughout the living host's body, interfacing with every cell while covering itself in a special film so the immune system can't attack it. Once the host's body temperature drops below a certain point after death, the parasite rouses from dormancy and sends microscopic tendrils through the epidermis to absorb oxygen from both air and water (which is how the walkers can survive underwater and without lungs). Via the parasite's circulatory system, the absorbed oxygen—as well as nutrients from ingested flesh—is transported around the walker's body to fuel its nervous system and musculature.
A submerged zombie head surveying its surroundings
Limited circulation still takes place in the walker's cardiovascular system via skeletal muscle contraction, both to supplement the parasitic circulation and to keep too much blood from pooling in the extremities. Chemicals secreted by the parasite also slow the growth of any necrotizing bacteria. Thanks to these redundancies, walkers can function for years while intact and well-fed—or at least several months as just severed heads—until they shut down from starvation.
As for why humans die from walker bites: a deadly cocktail of oral bacteria and a neurotoxic venom produced by the parasite.