Caution: spoilers ahead for Walking Dead: World Beyond
For the past 11 years, The Walking Dead's zombies have been the slow and lumbering kind but, unfortunately for the remnants of humankind, that particular rule no longer applies. The zombie genre is filled with all kinds of undead variations, but The Walking Dead has always subscribed to the classic "Romero" model. These monsters are reanimated corpses who have lost their ability to reason, as well as much of their motor function. Staggering around aimlessly in search of flesh is all they can manage, and it's this common brand of zombie Rick Grimes and co. have been battling since The Walking Dead began in 2010.
The Walking Dead: World Beyond's finale post-credits sequence has seismic consequences for the wider Walking Dead franchise. For starters, the scene confirms a French laboratory as the origin point for the zombie outbreak, revealing how a team of scientists manufactured the virus for as-yet-unknown purposes. There's also a video cameo by Noah Emmerich's Dr. Jenner from The Walking Dead season 1, recorded before his encounter with Rick Grimes. Jenner expresses concern over "variant cohorts" that have been reported in France, but aren't present in the United States.
The post-credits sequence then reveals precisely what he meant - fast zombies that are also smarter than The Walking Dead's typical monsters. World Beyond's final scene shows a scientist shot by another survivor as punishment for her role in creating the virus. As you'd expect, her corpse soon reanimates, jolting into life just as Walking Dead viewers have seen countless times before. Instead of slowly shuffling her way around the lab, however, the undead scientist begins running at pace, showcasing a new completely new type of zombie in The Walking Dead. These creatures are akin to zombies in World War Z, Zack Snyder's Dawn of the Dead, or the rage-infected in 28 Days Later. If that wasn't bad enough, World Beyond's variant zombies also appear smarter than usual. Instead of wandering around aimlessly until roused, the dead scientist runs straight for the lab's exit and hammers on the door desperately. Possessing the wherewithal to determine an exit route proves these zombies are fast and intelligent.
Walking Dead: World Beyond neglects to detail how these evolved zombies came about, but drops enough clues to piece together a rough sequence of events. The French solution mentioned by Dr. Jenner's video involves, "Steroidal therapies to jump-start the circulatory system in hopes of... regaining function." Cutting through the science jargon, that sounds suspiciously like turning inactive parts of a zombie's brain back on again. Maybe the French scientists believed they could reactivate zombie brains, but the trial ended up making the undead faster and smarter, triggering a mutation in France's virus. That would explain why the cigarette-puffing attacker claims the scientists "made it [the virus] worse," and also why these variant zombies have been present in France since The Walking Dead season 1, but aren't seen whatsoever in the U.S.
Alternatively, the evolved zombies in World Beyond's post-credits scene may solve an old 11-year-old plot hole. Back when The Walking Dead was still settling into its groove, the opening episodes featured undead that were a touch smarter than usual - hitting things with rocks and politely opening doors using the handle. Perhaps the French scientists merely accelerated a rare mutation that occurs naturally, making the variants far more common than they would've been otherwise.
The addition of zombie variants to The Walking Dead is a huge step forward for the franchise, and a strong indication of the direction AMC's flagship property is heading. Walking Dead: World Beyond's post credits doesn't show whether these evolved zombies are exclusive to France or have spread further into Europe, but it's surely only a matter of time before the same strain hits American shores, bringing a whole new edge to the apocalypse.