Zombies

Zombies are the main non-human antagonists of The Walking Dead. The zombies are the classic slow walking Romero style zombies, which originated in Night of the Living Dead. Following classic Romero-rules, everyone who dies, for any reason, will re-animate as a zombie. Even someone killed by a gunshot wound with no zombies involved at all, will re-animate as a zombie. Zombie bites are not how the "infection" is spread, its just that zombie bites and zombie slobber cause infections that are 100% lethal. Characters have speculated, but cannot confirm, that what ever causes zombies to re-animate is some sort of virus that everyone in the world is technically infected with, but which is only triggered by death.

The zombies out-number humans 5,000 to 1.

Behavior
Besides eating humans, zombies have been shown eating the horse Rick used to reach Atlanta, and a deer in the woods outside the original survivor camp. This also follows one of the variants of classic Romero-style zombies: some zombies from other science fiction narratives actively prefer to eat only human brains, or more generally, try to eat any part of a human but ignore animals. Romero's more realistic rules, established in Dawn of the Dead, are that zombies are just compelled to attack and try to eat any "warm bodies" they come across, regardless of whether they are humans or animals. in some television shows zombies say "brains" and only eat brains but in this show they eat any type of meat or organs

Herd

 * Main Article: The Herd.

As described by Dr. Eugene Porter, a herd is when zombies act with a mob mentality. One zombie might bang the side of a house causing another zombie to think there is something inside. Yet another zombie will notice and soon a chain reaction occurs where a large group of zombies have gathered.

Types
Zombies are separated by the survivors in the following groups:

Roamers
Roamers are known to "roam" around looking for food. They are the most commonly encountered kind of zombies.

Lurkers
Lurkers are the zombies that just sit around playing "dead" until someone reaches them and they bite them. Lurkers can be the real threat because they can pass as dead zombies. One of them was responsible for Allen's death and Dale losing a leg.

Biters
Alice, Dr. Stevens' assistant in Woodbury mentioned that her original group of survivors refered to the zombies as "biters," because while some do lurk and some may roam they all will bite and to classify them into separate groups is a silly practice.

Weakness
Zombies are only vulnerable to massive brain damage, (i.e. Shooting in the head). Zombies that are decapitated will keep their head alive until destroyed. The first zombie encountered by Rick Grimes outside of the hospital appeared to be immobilized after some kind of decay. Zombies are shown to be frozen, one almost bit Glenn. A zombie attempted to attack them, however he fell to the ground and didn't manage to stand up, it may be a sign that zombies can decay leading to the outbreak to finish in time.

Zombies seem to differentiate living humans from the undead via smell. Rick and Glenn are able to walk through an infested city to search for supplies after covering themselves in a zombie's entrails. Michonne is also able to walk vast distances without hindrance probably due to the fact the two defenseless zombies she kept near her dampened her scent. However due to the disgusting odour and the possibility of it washing off it doesn’t make it very practical for everyday application.

Kirkman wrote:
 * "[Zombies cannot usually go up stairs]--it's decided on a case by case basis...I'm sure there's a zombie out there who could...but not very well...to reference this series--was it issue 8? Rick opens the door to the basement of that house--and zombies are waiting at the top of the stairs and rush him!...So based on that scene...zombies can go up stairs... but it probably took them a while."

Strengths
Zombies main advantages over humans is that they do not need to sleep, eat or breathe. This allows them to slowly follow the survivors around in perpetuity (or until they decay to the point of no longer being mobile or otherwise threatening)

Infection and Amputation
As shown in the case of Dale, a person can survive a zombie bite if the limb which is bitten is amputated.

Robert Kirkman wrote:
 * "...the rule is: WHATEVER it is that causes the zombies, is something everyone already has. If you stub your toe, get an infection and die ... you turn into a zombie. UNLESS your brain is damaged. If someone shoots you in the head and you die ...you're dead. A zombie bite kills you because of infection, or blood loss ... not because of the zombie "virus.""

Evolution
Robert Kirkman wrote that "Romero's evolving zombies are his spin. Mine just keep rotting."

Zombie animals
For some reason animals are not affected by the virus, but nobody knows because they are eaten whole. Kirkman has stated there are no zombie animals.

Trivia

 * In Issue 38 Robert Kirkman writes there is "ONE zombie who's appeared no less than three different times in the book"
 * Michonne kills a zombie going into a car with a t-shirt that says "Youngblood"
 * In the TV Series, some of the survivors, notably Glenn, refer to the zombies as "geeks".

Credited Zombies

 * Addy Miller as Little Girl Zombie, the little girl found at the gas station in Days Gone Bye.
 * Brian Stretch as Tank Soldier, the undead soldier in the tank, from Days Gone Bye and Guts.
 * Joe Giles as Black Suited Zombie, the zombie wandering in the street when Rick emerges from his empty home in Days Gone Bye.
 * Melissa Cowen as Bicycle Girl Zombie, the half-zombie crawling in the park in Days Gone Bye.
 * Max Calder as Baseball Bat Zombie, the zombie that Rick kills with a baseball bat in Days Gone Bye.