Zombies were nothing new when The Walking Dead was unleashed upon the world, but Robert Kirkman's series definitely added to the genre. Every depiction of zombies is different, even if they all follow the same singular premise: reanimated corpses that enjoy feasting on the living.

To make a series interesting, it's important for a creator to add or even take away from the established genre. With more than 180 issues and nine seasons of the series on television, there's a lot to learn about the zombies of The Walking Dead. Here are 10 things we know about the undead from the series.

THEY'RE ATTRACTED TO SOUNDS

The Walking Dead Zombie

Soon after the dead rose and began to feast upon the living, those who survived picked up on a key feature, which helped them to survive. The dead respond to sounds more so than visual stimulation or even physical touch. This was especially true of zombies whose eyes were no longer present or functioning.

Moving quietly among the dead is important if you want to survive, and firing off a gun is especially dangerous. This is one of the main reasons the survivors get in close with clubs, swords, hatchets, and other similar weaponry. Killing a few at close range is preferable to being surrounded by hundreds.

THEY CONTINUE TO ROT

Walker - The Walking Dead _ Season 5, Episode - Photo Credit: Gene Page/AMC

The more scientifically literate viewers of the AMC series know that a walking corpse won't last long in the Atlanta sun. Human bodies begin to rot almost immediately upon death, but the zombies wouldn't be much of a threat if they crumbled to dust in a matter of days or weeks.

To keep things mildly close to accuracy, they do continue to rot; the longer a person has been dead, the nastier they get. This has been evident in the comics, but even more so on the show. The dead have far fewer parts and much less skin in season nine than they did in the pilot episode.

THEY DON'T FEED ON THEIR OWN KIND

The Walking Dead Walking amongst the Zombies

The dead walk about until they find something to eat, but otherwise, they don't do much. If an animal or person crosses their path, they will become active and attempt to eat them, but if that doesn't happen, they won't start biting one another to sate their hunger.

This was not only apparent to the survivors, but it also proved to be a valuable tool in keeping from being eaten. If a person is willing and able to do so, they can cover themselves with gore and walk among them with impunity... they just need to remain quiet and move slowly.

A BITE WILL ALWAYS RESULT IN DEATH

The Walking Dead Zombie Eating a woman's face

Every living person in The Walking Dead universe will one day become a zombie, but that doesn't mean they are all sick and dying. That changes the moment they are bitten — even if it's just a little nibble on the toe. A bite will always result in an illness with a 100% fatality rate.

This is one of the main reasons it is so vitally important to keep your distance while fighting zombies. A scratch may also lead to the dreaded infection, so any contact should always be limited to the greatest extent possible. Get too close, and you will become a zombie far sooner than you might have liked.

EVERYONE TURNS AT DIFFERENT RATES

Fear the Walking Dead Zombie newly turned

Thanks to a quick stop at the Centers for Disease Control and Prevention in Atlanta on the series, the rate at which people turn was revealed. This wasn't described fully in the books, but according to Dr. Jenner, a victim will turn in as much as eight hours after death, and as quickly as three minutes.

Because the time is unknown and there is no way to determine it beforehand, the survivors have developed a strategy to protect themselves. As soon as someone dies for any reason, they are stabbed, usually in the base of the skull, to ensure they never turn into a zombie.

THEY MERGE INTO HERDS

The Walking Dead Zombie Herd

In most cases, a zombie will sit around and do nothing until they have a reason to move. They might otherwise mill about on their feet, but for the most part, they linger in any area where they were last drawn. When they hear something, they move towards it and this results in the formation of herds.

A herd will form when zombies continuously follow one another towards a perceived meal. They continue moving as they gather more and more individuals, which ultimately results in a mass of the dead often numbering in the hundreds, and in some cases, thousands.

THEY WILL EAT ANY LIVING FLESH

The Walking Dead Zombie Eating Guts

People are the principal characters of the book and television series, but they are hardly the only thing a zombie will stop to eat. Whenever any living creature stumbles along their path, a zombie will make every effort to eat it. This was immediately apparent in the first season when Rick met a herd while on horseback.

When the horse threw him, it was immediately mobbed by dozens of zombies who quickly ate it. Later in the series, Rick lured a group from the prison with some pigs he hobbled for that purpose. They don't appear to have a preference, just that the meat is fresh and alive when they begin to eat.

THEIR BRAINS KEEP THEM GOING

The Walking Dead Maggie killing a zombie

Anyone who's enjoyed the genre over the years knows that the only real way to put down a zombie is to take out its brain. This characteristic has led the group of survivors to be better at racking up headshots than any other group in all of fiction.

Cutting off the head isn't enough to take one of them out, though it does immobilize the body. That said, the head can (and will) still bite, which makes for a lethal object if left on the ground. Shooting, slicing, and stabbing the brain into bits is the only way to ensure they won't keep coming.

THEY OUTNUMBER HUMANS 5,000:1

The Walking Dead Zombie Herd tv show

Because the Internet is full of fans and math nerds, occasionally the two groups meet to create a person capable of quickly calculating exactly how many people walk the planet as zombies. Assuming 10% of the population wasn't immediately turned, it's possible to take the number of people in an area like Atlanta today and calculate how many would be zombies tomorrow.

What the numbers show is that after a good number of people turn into zombies leaving a scant few survivors, the dead end up outnumbering the living by about 5,000 to one. Given those numbers, the first season pitted the survivors around Atlanta against approximately 390,000 zombies.

THEY AREN'T CALLED ZOMBIES

The Walking Dead Zombies

One of the key differences between the universe of The Walking Dead and every other depiction of zombies is that they aren't called zombies in the books or on the show. To be fair, it slipped past the editor once or twice in the books, but for the most part, the word is never uttered. This has been explained by saying the world never had the word before the apocalypse.

NEXT: The Walking Dead's Zombie Twist Explained

Whatever the reason, it has given the writers a great opportunity to come up with alternates. Each group of survivors has their own name for the dead including the main group's Walkers alongside others like Biters, Geeks, Creepers, Cold Bodies, Dead Ones, Floaters, Lurkers, Lamebrains, Monsters, Roamers, Skin Eaters, and Rotters.