Every season on “The Walking Dead” we’re introduced to new characters, new threats, and tons of new zombies who only continue to get more gruesome.

Though the show has been on the air since 2010, only about two years have transpired in the zombie apocalypse, according to executive producer and make-up supervisor Greg Nicotero.

That’s helped slow down the decaying process a bit, but Nicotero and his visual effects crew continue to evolve the look of the walkers, as they’re referred on the hit AMC series, each year.

“Every season we take advantage of the advancement of our timeline,” Nicotero recently told Tech Insider. “It’s definitely something that we try to push in terms of more skeletal [looks], sloughing off skin, missing noses, exposed ribs, exposed organs, all that stuff. Anything that we can do to further and continually suggest that these are walking, emaciated, decomposing corpses that have been wandering around in the sun, wandering around in the rain, wandering around in the elements for almost two years now.”

While many walkers may be missing limbs now, they didn’t always look this frightening.

In season one, we’re introduced to the zombie apocalypse about four to five weeks after it has begun.

The first walker we’re introduced to on “The Walking Dead.” AMC

Clothes are pretty much intact, and from far away, most zombies could pass for regular people.

AMC

Special effects makeup artist and current executive producer Greg Nicotero and his team from KNB EFX used Robert Kirkman’s graphic novel for inspiration.

Nicotero works on one of the walkers for season one. Scott Garfield/AMC

The crew looked for a specific physical type when casting extras. According to Nicotero, they needed to be tall, thin, and really gaunt.

AMC

“In all of Charlie [Adland]’s drawings there’s always teeth so a lot of our hero characters [zombies with full prosthetics] we made dentures that clipped over their lips and then the prosthetic pieces covered the edges of the dentures so it appeared as if the lips had either stretched away or rotted away.” said Nicotero.

AMC screencap

The eyes were also very important. “Some of the lenses were bloodshot, some of them had cataracts, some of them were a little yellowish and kind of looked diseased,” Nicotero said.

AMC
Source: The Hollywood Reporter

As the walkers continue to decompose in season two, the eyes became even more important.

Gene Page/AMC

“It’s a little more gruesome,” said lens technician Gazal Tabrizpor. “You’ll see more bloodier contacts where the veins had ruptured. The drawing on them is a lot more vivid.”

Greg Nicotero/AMC
Source: AMC

Here’s a close-up.

AMC

While zombies still look relatively human, an update was also made to dentures worn by walkers as flesh began to tear away more.

AMC

When season three premiered in late 2012, zombies began to look noticeably more gaunt.

Gene Page/AMC

Eyes began to look even more sunken into faces.

Gene Page/AMC

There was a focus on walkers looking more rotted and decayed.

Gene Page/AMC

“This season, one of the things that we wanted to do was to be able to bash, crush, smash, just destroy some of our walkers,” said Nicotero. To produce the practical gags, a number of hollow zombies were made to splatter blood.

AMC
Source: AMC

Nicotero and his effects team also added the use of more animatronic puppets like this one with a moving head.

Greg Nicotero with one of his animatronic zombies. AMC

By the end of season three, there was further discoloration and deterioration to the skin.

Gene Page/AMC

Moving into season four, zombies began to decompose even more.

At the start of the season, fans have estimated we’re approximately 321 days into the zombie apocalypse. Skin has sagged and dried out.

Gene Page/AMC
Source: The Walking Dead wiki

Hair begins to diminish.

Gene Page/AMC

We also saw our first completely charred walker.

Gene Page/AMC

Walkers are more prone to falling apart and looking decrepit in season five.

Gene Page/AMC

It’s more common to see noses missing.

Gene Page/AMC

Clothes are tattered and disintegrating. Bodies, especially those exposed to water, are appearing more skeletal in structure.

Gene Page/AMC

“More and more skin decomposes, more and more bone structure and skeletal traits are visible; sometimes the teeth are broken out; sometimes their beards and their hair grows a little bit longer; sometimes their limbs are missing,” says Nicotero.

Gene Page/AMC
Source: The Frame

By the second half of season five, walkers are not looking human anymore. They’re becoming mere skin and bone — or close to just bone.

Gene Page/AMC

Now, on season six, Nicotero continues to push boundaries.

Gene Page/AMC

We’re seeing some of the most frightening walkers yet.

Gene Page/AMC

Nicotero told Tech Insider walkers will have more moss and branches growing on them in addition to skin sloughing off.

Gene Page/AMC

We’re sure we’ll see even more terrifying zombies as the season continues. But one thing’s certain.

Gene Page/AMC

“The only thing you’ll never see is a … perfectly-clean skeleton walking around because obviously, there’s no muscle,” Nicotero told us. “We still try to keep to the reality of there needs to be muscle to move the bone to move the body.”

Gene Page/AMC