There's one type of zombie you'll never see on 'The Walking Dead'

Greg Nicotero/AMC

The INSIDER Summary

• We've seen a lot of walkers decay throughout "The Walking Dead" series.
• Executive producer Greg Nicotero tells us there's one extreme type of zombie you won't see on the show.

Over the course of six seasons, "The Walking Dead" zombies have lost flesh, hair, noses, and more appendages.

But as the walkers continue to rot under the direction of makeup mastermind and "The Walking Dead" executive director Greg Nicotero, there's one way you'll never see the zombies: as skeletons.

"The only thing you'll never see is a Ray Harryhausen[-inspired], perfectly clean skeleton walking around because obviously, there's no muscle," Nicotero told us last year ahead of the show's season six premiere.

Nicotero was referring to visual effects pro Ray Harryhausen, who is known for pioneering stop-motion effects in films like "The 7th Voyage of Sinbad" and 1963's "Jason and the Argonauts."

Here's a look at some of his zombies from the latter film:

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"We still try to keep to the reality of [needing] muscle to move the bone to move the body, but it's just something that we continue to push every season with new sculptures and pushing the elements of what we can," Nicotero explained.

"Every season we take advantage of the advancement of our timeline and the advancement of our story and it's definitely something that we try to push in terms of more skeletal sloughing off skin, missing noses, exposed ribs, exposed organs ... all that stuff," said Nicotero. "Anything we can do to just 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."

Nicotero said some of the ways they've done that is by having moss and branches growing on zombies. If you've been paying attention to the walkers in season six you'll notice there were a few moss-covered zombies.

Gene Page/AMC

Some zombies from season six of "The Walking Dead."

Gene Page/AMC

"Something that we do every so often is we will augment practical effects," said Nicotero. "A good example is when Hershel's head was cut off in season 4. We had a practical animatronic head with jaw movement and we put digital eyes on it so that we were marrying the two techniques to give us something a little different."

AMC / The Walking Dead

Hershel before his death in "The Walking Dead."

Gene Page/AMC

Behind the scenes of Hershel's death in season 4.

Nicotero said he always wants to keep viewers guessing.

"I always want the audience to sort of scratch their head and go, 'Wow, that looked like real eyes. How did they do that? Did they cut a hole in the ground and put Scott Wilson's body in the ground or did they do an animatronic or was it all CG?' I love when people ask those questions so in this season, there are a few instances where we have done that, where we removed a nose and we removed part of a face or we made the waist or the torso ... we accentuated the rib cage and made it super thin. So, it's basically using both techniques to further a visual style that we've been looking for."

"The Walking Dead" will return to AMC for its seventh season October 23 at 9 p.m.