Common to virtually all Zombie Apocalypse tales is that, regardless of the reason zombies attack living/non-infected people, they usually never attack other zombies. This makes some sense in stories where the zombies are manipulated by some force intent on attacking humanity, or where they need fresh human meat to survive, but it occurs even in films like 28 Days Later where The Virus is just supposed to make the infected vastly more angry and homicidal than before. They can sometimes be seen fighting for food, but this never goes beyond pushing each other out of the way. Why they never turn on their own is rarely, if ever, addressed, though some works have cared to do so and provide various explanations, ranging from infected flesh being unappealing to The Virus compelling zombies to attack and infect living targets in order to spread it. Some stories take this all the way to the point that ordinary humans can avoid being attacked by pretending to be zombies.
Any truly large-scale zombie apocalypse is likely to demand a heavy degree of Hollywood Tactics or handling of the Idiot Ball by the military. Against any sort of heavy or explosive weaponry, the unprotected human body is not simply wounded, but ripped apart. For that matter, armored vehicles like tanks would be completely invincible against an unarmed foe, and weigh enough to crush bones merely by running something over. Rarely will any of this come into play. There is some justification under the Romero rules as any death renews the problem, including within a previously secure area. Depictions where zombiism is The Virus may avoid the issue by noting that, eventually, the problem is contained and dealt with. In World War Z, there is an attempted Handwave along the lines of zombies not feeling pain or fear, and the military caring more about looking good for the media, but this, at best, badly underestimates the ability of modern ordnance to blow organic matter apart wherever it hits.
Overwhelmingly, zombie apocalypse stories tend to fall into one of two categories of political allegory. The zombie horror can be used to make a political statement against consumer capitalism and humanity's most violent, rapacious, self-destructive habits made literal, with zombies representing the bulk of humanity as unthinking (flesh-eating) sheep (zombies in the mall, anyone?). The other strain of zombie horror advocates hardcore individualism and libertarianism, again with the zombies as the "unthinking masses" but with an added emphasis on the heroic "well-prepared" survivalist, with Karmic Death to anyone who dares show compassion for others or cares about anything other than their own personal survival. In both versions, anything that would be considered conventionally patriotic is right out; the military, the government, and corporations are rarely anything but obstacles at best, and actively evil at worst. Strangely, though zombies seem to fit the "aliens as communists" archetype, pro-capitalist, anti-communist zombie apocalypses are less common.
Many Zombie Apocalypse stories are based on a mixture of two major rulesets, one codified by George A. Romero and the other codified by John Russo, with an emphasis on "based on" as both Romero's and Russo's zombies break modern zombie conventions in certain ways.
The classic "Romero Rules" for zombies include:
- Whatever the cause of zombiism, the effect is pandemic. Anyone who dies arises moments later as a zombie, regardless of the cause of death, unless they suffer damage to the brain or are immolated by fire.
- The bite of a zombie is infectious and is always a fatal injury, even if it seems like a trivial scratch. This results in the victim returning as a zombie, much to the horror of the Zombie Infectee, though this is essentially coincidental as zombification occurs every time someone dies, even if the victim never had any zombie-inflicted injuries in the first place. This rule is probably the source of the confusion between the first rules of the Romero and Russo rulesets.
- Zombies are slow-moving and slow-thinking. That said, Romero zombies are an unbuilt case as in their very first movie Night of the Living Dead, they are capable of rudimentary tool usage, problem-solving, and some memory recall, and the sequels show them growing smarter over time. Later zombie movies, including game-changers like 28 Days Later that subvert zombie standards, tend to keep the zombies mindless since adherence to Romero's portrayal makes the zombies too human or too intelligent for the survivors to deal with.
- Zombies are not significantly stronger than humans, though they are not disadvantaged by pain, injury, or fear as humans are.
- It is generally the case that a single zombie is not a tremendous threat, owning largely to the previous two rules. The threat of zombies generally stems from the fact that they tend to turn up in mobs.
- Zombies can be killed only by destroying their brains or destroying their entire body although rendering them immobile, such as through decapitation or dismemberment, is generally just as good. In The Zombie Survival Guide, Max Brooks points out that, since zombies can't feel pain, a burning zombie will simply keep moving around (and setting other stuff on fire) until they become immobile. Also, while beheading a zombie will immobilize it, the head itself can still be dangerous if one isn't careful
- Zombies are compelled to eat the flesh of the living.
The "Russo Rules" are similar, but include several specific differences:
- Zombiism is The Virus. Zombiism only spreads through zombie bites although the patient zero zombies may have had a different way of acquiring the virus. Most non-Romero zombie films prefer this convention to Romero's, including the 2004 remake of Romero's Dawn of the Dead, because there is more potential drama to be mined from the survivors avoiding zombie-inflicted damage at all costs to prevent zombification.
- A zombie bite results in zombification although the transition is slow with the victim becoming progressively more zombie-like until they fully zombify, at which point the victim becomes another predatory zombie and turns on their former human allies.
- Zombies are more obviously intelligent, enough that they are basically normal people who happen to be undead. That said, they still have to resist their urges if they don't want to hurt any humans. As with Romero's portrayal of zombie intelligence, plenty of zombie works ignore Russo's "smart zombies" as well; on the other hand, zombie romance stories with a Boy Meets Ghoul or Resurrected Romance plot use Russo's revenant zombies.
- Like the average human, Russo zombies can talk and can fool humans into believing that they are fellow humans. Pop culture exaggerates this rule to depicting zombies that can only repeat the word "brains".
- Zombies are stronger than humans and can be capable of running. Due to their undead nature, zombies can be nigh-impossible to destroy as they don't need their brains to function, and dismembering/decapitating the zombie is futile as well because the zombie's limbs are able to move on their own.
- Zombies are specifically compelled to consume the brains of living humans. Russo zombies eat brains to ease the pain of their deterioration as the brain contains endorphins, which are painkiller chemicals. However, pop culture reinterprets this rule as zombies eating brains to increase their intelligence as depicted in zombie media like Warm Bodies and iZombie.
Often, zombie apocalypse stories are tied with a Science Is Bad message, or an allegory about human nature. (Night of the Living Dead (1968) contained an allegory for race relations, though Romero stated that it was unintentional. Its sequel, Dawn of the Dead (1978), skewered American consumerism.)
The Zombie Apocalypse is so iconic that perfectly sane people will formulate emergency survival plans in case of shambling corpses. There are also survival guides available all over the web and in print. The explanation occasionally given for this is if one is sufficiently prepared for the complete collapse of societal order and infrastructure and the almost spontaneous appearance of unending hordes of hostiles with a quick and simple method of conscription, one is effectively prepared for anything. Actual rescue agencies will sometimes have "Zombie Apocalypse" training exercises because it allows the people to brainstorm freely without causing political turf wars or falling into routine ideas (and because professional rescuers have dark senses of humor). And be honest, you know that you would secretly love for one to happen.
Zombie films have an ace in the hole for directors, too. The monsters are cheap. While you can use special effects to create them, all you really have to do is hire some extras, throw a little makeup on them, and voila! — instant monsters.
In reality, this situation is highly unlikely. A week-old corpse on a pleasant summer day, moving or not, will be fertilizer by evening. (Some works, like The Zombie Survival Guide, find ways around this by having The Virus slow decomposition.) It's also rather like going up against a bear every time you want to make a sandwich or mate from the perspective of the zombies, as their preferred choice of food and reproductive medium is also their greatest predator. And, as it has been noted in the quotes page, humans send robots to other planets, while zombies are befuddled by doorknobs and stairs.
