The new trailer for Daryl Dixon: The Book Of Carol released at San Diego Comic-Con just introduced another zombie variant to the franchise. It’s an easy moment to miss, given the influx of fresh content that always coincides with SDCC weekend. Towards the end of the video, there is a brief shot of a zombie illuminated by a bio-luminescent glow. This follows producer Greg Nicotero’s reveal that new zombie variants will be introduced in Daryl Dixon season 2.

Variants are part of a Walking Dead trend that has seen new evolutions of the classic walkers. So far, we have already seen smarter zombies introduced in season 11 of The Walking Dead. The first season of Daryl Dixon explains the origin of the super-strong zombie variants first revealed in The Walking Dead: World Beyond. Glow-in-the-dark zombies are something new, but these variants are actually a subcategory of a type that the franchise has shown before.

Why The Zombies Are Glowing In Daryl Dixon Season 2

Walking Dead Zombies Can Change With Their Environment

In this two-second shot from the Book of Carol trailer, a silhouetted figure (presumably Daryl) explores a darkened environment illuminated by glowing material. He comes across a walker whose skin is covered in patches of this strange substance. Blink and you’ll miss it. It’s not clear exactly what this glowing substance is – it might be a chemical off-spill, resulting in a toxic variant like the acid zombies from Daryl Dixon season 1, or the methane-mutant monstrosity in The Walking Dead: Dead City.

What’s clear is that these new glowing zombies have evolved as a product of their environment. They have likely ingested some of this toxic material and incorporated it into their physiology. This glow is probably more than a cool visual effect – every time The Walking Dead introduces a new variant it presents an added danger for the protagonists to overcome. Variants provide a way of renewing the original threat that the walkers pose after prior installments of the franchise made them secondary to human antagonists.

Daryl Dixon Season 2’s Glowing Zombies Continue A Walking Dead Trend

Each New Variant Has To Be Explained As The Universe Continues To Expand

This isn’t the first time The Walking Dead has shown zombies altered by their surroundings. In episode 5 The Ones Who Live, Rick and Michonne encounter a stone zombie variant, significantly more difficult to take down due to their hardened exterior. The show also introduced flaming zombies, though whether these fire zombies are true variants is debatable. The Walking Dead may get more outlandish as the franchise churns on, but randomly introducing elemental zombies would be a step too far.

Even the stone zombie wasn’t literally made of rock – no matter how wacky the walker evolutions it introduces, The Walking Dead at least makes an effort to provide a rational explanation for their appearance. The stone zombies’ hardened exterior is a by-product of the steam vents in the national park, which had “calcified” their skin. The science behind that may be a bit shaky, but then again, so is the entire premise of the show. It’s impossible to enjoy The Walking Dead without the suspension of disbelief, and it can be counted on that Daryl Dixon is going to supply an explanation for these new glowing zombies that tracks with the in-world canon.

Daryl Dixon’s Glowing Zombies Are Not True Variants

But True Variants May Also Appear In The Book Of Carol

Admittedly, these glowing zombies can’t actually be classed as true variants. Rather like The One’s Who Live’s rocky zombies, they are environmental accidents. Though they may offer a unique twist on the classic walker, there is nothing inherently different or unique about them. Their glowing appearance probably altered over time, but originally, these would have been human victims of the same contagion that made all zombies – the origin of the outbreak virus was explained in The Walking Dead:World Beyond.

To be a true variant, a zombie has to exhibit a difference in behavior. It could be intelligent enough to throw rocks, or open doors; it could be stronger and faster than your average, shuffling walker. Interestingly, true variants have been a part of The Walking Dead since it began. The very first zombie that Rick put down was a little girl who recalled enough about her past life to pick up her old stuffed toy. Whether these mutations evolve naturally over time or are the result of a separate strain altogether is yet to be properly explained.

The mystery behind The Walking Dead’s variants is something that Daryl Dixon season 2 could solve. Setting the series in France, where the laboratory that started the outbreak is located, is obviously more than mere coincidence. Now that the precedent is set, The Walking Dead is likely to continue the trend of introducing new variants, and we already know that France happens to be a hot spot for these strange new zombies. We can already assume that glowing zombies won’t be the only bizarre evolution that Daryl Dixon: The Book of Carol will introduce to the franchise.