No Zombie Cannibals

In zombie dinner parties, it's a bring yourself potluck.

"The normal question, the first question is always; are these cannibals? No, they are not cannibals. Cannibalism in the true sense of the word implies an intraspecies activity. These creatures cannot be considered human. They prey on humans. They do not prey on each other, that's the difference!"

—Dr. Millard Rausch, Dawn of the Dead

So you're a zombie (sorry to hear that, by the way). You have your daily routine; shamble, moan, be always on the lookout for live human flesh. And when that flesh appears, you and every other zombie in a hundred-mile radius will converge on it in one enormous mass of undeath.

But surely you're not satisfied with that, are you? There's not even close to enough to go around. One human divided among one hundred zombies is less than a meal.

And yet... isn't there still human flesh all around you? After all, the zombies are "human", just a slightly hungrier type of human, and most of the capacity for reason is gone. You still have to eat. Meat is meat. So what's to stop this horde from feeding on itself?

Ultimately, there is no reason; it just plain doesn't happen, and is left at that. We can only say for sure that there are No Zombie Cannibals. When The Virus creates zombies that are still technically alive, there's no perfectly sensible explanation. Additionally, no matter how ravenous, the zombies will cooperate, instead of fighting over the scraps.

When it is addressed and sketchily justified, it's usually that zombies will only eat living flesh because undead flesh is "not nutritious" or otherwise appealing, The Virus gives them an instinctive sense to go only after uninfected, or that they're supernatural undead, and thus know not to eat each other and instead cooperate. You can certainly argue that rotting flesh wouldn't be terribly safe to eat, but that would bring up the question of why it can walk around in the first place.

Sometimes lampshaded when the heroes Pretend They're Dead in order to pass. A Zombie Infectee or Vampire Refugee may be able to pretend to be a zombie and get ignored.

So ubiquitous it's probably better to list aversions, or explicit justifications. See also Gang Up on the Human, the Video Game AI version.

Examples of No Zombie Cannibals include:

Justifications

Comic Books

The Marvel Zombies indicate that zombie flesh not only tastes horrible, but does nothing to satiate their hunger.
- Even alien zombie flesh doesn't help. But uninfected alien flesh is perfectly delicious.

Film

In REC, all the 'zombies' are controlled by a demon, so it makes them cooperate and even hide. Weapons use was more limited though.
In the Resident Evil movies, the manual states that zombies chew on the living because they hunger for life, rather than flesh. They last for decades before decaying, with food or without.
In the tie-in graphic novels that bridge the gap between 28 Days Later and 28 Weeks Later, it's stated that the Infected don't attack each other because they all give off the same pheromone—i.e., they all smell the same to one another, whereas uninfected smell like ordinary people. One character who figures this out survives by finding a way to negate his natural human scent, and later draws a mob of Infected to attack a rival survivor by lobbing a bomb of perfume on him. Why exactly the pheromone stops the Infected attacking one another is never properly explained, though.

Literature

In The Zombie Survival Guide and World War Z it is mentioned that Solanum causes the flesh of the victim to become highly toxic. Naturally this does not harm other zombies, but may explain the lack of cannibalism if the toxic flesh smells different. In World War Z many people believe they have witnessed zombie-on-zombie attacks; it is revealed that the victims of these attacks were actually "Quislings", people suffering a mental breakdown caused by the Zombie Apocalypse who believe they are zombies themselves... while other people can mistake them for the undead, the real zombies are not fooled.
- It's also noted that they don't fight each other because they simply don't perceive anything other than living creatures. A zombie that wants a chunk of human that another zombie wants will keep pulling on it rather than shoving the other zombie away.
In the Star Wars Expanded Universe novel Death Troopers, the zombies are all controlled by by a psuedo-organic hivemind sludge that the Empire was experimenting with. The sludge, called Project Blackwing, is heavily implied to be sentient, and wishes to spread itself as far as possible.
Justified in Elantris the flesh of the psuedo-zombie Elantrians tastes so terrible that despite their constant ravenous hunger they can't bear to eat each other.

Aversions

Comic Books

Strangely enough though, the Marvel Zombies are not above fighting each other for the scraps. In fact, pretty much ninety-five percent of the entire horde are destroyed by their leaders (Colonel America and the main five Marvel Zombies presnt in MZ 2 onwards) when they gain cosmic powers after devouring the Silver Surfer.
The comic version of Hellgate:London had one of the characters belong to the Cabalists, a separate faction of Bad Powers, Good People who use black magic and the demons' powers against their enemies. She uses her arcane powers to coerce a rampaging hoard of reanimated undead into believing there was plenty of food among them and devour each other.

Film

In Night of the Living Dead: zombies do fight among themselves for their meals.
In ZA:Zombies Anonymous: zombies who refuse to eat living humans are eaten by the cult of zombies who will.
In 2013's Warm Bodies, there are two kinds of zombies—shuffling "walking corpses" and the faster, feral and skeletal "skinnies"; while the "fresher" zombies don't attack each other (and indeed, still seem to hold on to some kind of "society"), the skinnies show no hesitation in attacking anything humanoid, living or dead.

Literature

Early on in Stephen King's Cell the "zombies" attack each other, but this disappears when they develop a hivemind.
In Mira Grant's NEWSFLESH trilogy, (in "Feed," in particular,) we find that zombies prefer to attack the living, but will attack and consume each other if starving.
Diario de un Zombi has Erico, the lone thinking zombie, explain it's the sensation of life they crave. That said, zombies are dumb as bricks and do eat themselves or others if desperate, confused or angered.

Live Action TV

The Wraith of Stargate Atlantis aren't strictly zombies, but they do need to eat humans. One episode did show them as capable of endocannibalism, but since they're intelligent that's probably either taboo or just not a good species-survival strategy (the one who did it was stranded and starving).
The zombies in The Walking Dead also seem to hunt by smell, as two men are able to pass among them undetected by covering themselves in zombie blood and guts. Once a rain shower washes them clean, however, the zombies catch on.

MMORPGs

Urban Dead: zombies can attack each other for XP, though they only gain half of what they get for damaging human players. Still, "cannibalism" is a good way for a new zombie to gain experience.
In World of Warcraft, the playable Undead have cannibalism as a racial ability, and it works on both humanoids and other undead.

Tabletop Games

GURPS: Infinite Worlds has Gotha-zombies, which do eat each other.
The fan-made Zombie: The Coil for the Old World of Darkness has two breeds of zombie: Grandes, which can only eat living flesh, and Jackals, which can eat any decayed flesh. This includes other zombies. The two breeds, of course, do not get along. (Sidenote: this book was created several years before Bleach...)
In Magic: The Gathering, there indeed are Zombie Cannibals.

Video Games

In Left 4 Dead 2, you can make the zombies fight amongst themselves using boomer bile. Only half of an aversion, as are simply Zombie Classic at every other time.
- Not entirely true. In L4D1 you will occasionally come across infected fighting each other.
  - However, it's still a subversion. There is infighting, however, these are not human eaters. They have an advanced form of rabies, which has induced rabies symptoms, just tenfold. The reason they are fighting is because they are literally insane. Word of God.
  - L4D2 keeps the infighting mind you, it's just rarer to see. Also note that there are some occasions of the mutated zombies fighting each other, like the Tank knocking the Witch dead in order to get to the survivor.
  - And another note: the zombies aren't actually eating the survivors either, as far as we can see, it's more that they want them dead. A lot.
Averted in Warcraft 3. Ghouls will eat any killed units to restore health, whether previously alive or undead. Lack of infighting is due to Mind Control.
Zombies are occasionally seen eating other zombies in the Resident Evil series. (Pre-RE 4 at least.)
Played straight and then inverted in the tie-in graphic novel for Hellgate:London, where a horde of ravenous zombies cooperate until the demon-infused sorceress of the party they're attacking uses her magic to convince them that there is plenty of food already to eat (themselves) and they kill each other.
Often averted in Urban Dead: Zombies attacking each other earn only half XP, but it can still be faster than hunting humans at low levels and is even officially endorsed by some hordes. And they can't permanently kill each other anyways. At higher levels the fact that they attack only humans is simply a consequence of the fact that "they know better than to eat each other" is true on a meta level; they're all controlled by real players.

Webcomics

In Zombie Ranch these two pages explain that the zombies won't eat each other under normal circumstances, but it's standard practice to recycle destroyed or non market-worthy zeds into feed for the rest of the herd.

Web Original

On We're Alive, the zombies carry away the bodies of their dead. It is later revealed that they keep stockpiles of human flesh for food and may be eating their own dead.