Common to virtually all Zombie Apocalypse tales is that, regardless of the reason zombies attack living/non-infected people, they 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. Why they never turn on their own is rarely, if ever, addressed, although sometimes they can be seen fighting for food, but this never goes beyond pushing each other out of the way. This can be subverted if 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, and quite possibly within a 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 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, 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.
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, whatever the cause of death, unless they suffer damage to the brain.
- The bite of a zombie is infectious, and is always a fatal injury, even if it seems 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 would equally result had the infectee died of, say, rabies. This rule is probably the source of the confusion between the first rules of the Romero and Russo rule sets.
- Zombies are slow-moving, lumbering, and stupid. Subversions of this have only recently appeared, but are increasingly common. In the Romero canon, it is a recurring theme that zombies become cleverer as time passes.
- Zombies are not significantly stronger than humans, though they are not disadvantaged by injury 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, as by immolation, which results in the same thing), though rendering them immobile is usually taken to be 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.
- 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 results only from being bitten by another zombie, though event zero created the first zombie that starts off the chain reaction. Most non-Romero zombie films prefer this convention to Romero's, including the recent remake of Romero's Dawn of the Dead.
- A zombie bite results in zombification, though the transition is slow, with the victim becoming progressively more zombie-like. Zombies become stupider and less human over time, presumably as their brains decompose. A "recent" zombie may be able to suppress his monstrous tendencies for a time.
- Zombies are stronger than humans, though they remain slow-moving. Zombies are nigh-impossible to destroy, being vulnerable to damage to the brain as above, and immolation though this can also release The Virus.
- Zombies are specifically compelled to eat the brains of living humans. Zombies still possessing the power of speech may begin talking rather obsessively about smelling brains, before their minds deteriorate and leave them saying only, "Brains..."
- They say "brains" because Russo zombies find being dead very painful, and eating brains is the only thing that eases that perpetual agony.
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 CGI, etc for them. all you really have to do is hire some extras, throw 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. 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.