11. The US is quarantined - because the virus is a botched military weapon
What it means: The USA is the only country to have fallen under the zombie regime, according to this theory. The reason? A military experiment that went horribly, horribly wrong. Fans suggest that a biological weapon was either intentionally or accidentally released, it infected the public, and the US had no way of controlling the subsequent outbreak of flesh-eating groaners. North America is quarantined to prevent the spread to other continents.
That would make for a killer ending of the show: to discover that the entire time the remainder of the world has been happily ticking along, letting North America fall. Sonequa Martin-Green, aka Sasha, even has a concept for how that would play out in the series finale: "How about last shot, last everything, whoever's there, we get to the coast, you pan out, and you see all this ships blockading, in which you find out that it's just America."
Military shenanigans a la the X-Files? This shimmers with a hint of truth. Especially as sister show Fear the Walking Dead kicks off with a bold military presence, as if to imply that the government knew what was happening all along...
12. Eugene is responsible for the outbreak
What it means: Eugene is actually who he says he is. Sort of.
Way back when we first met Eugene, we learned that he worked on the Human Genome Project and knew of a virus cure. The mulletted oaf told a massive lie to keep himself safe. Then the truth emerges in season 5. He confesses, revealing that he's not a scientists. BUT he does say that he "knows things."
This makes sense when you consider the fact that he also admits to being a "very good liar." If that's true then it's impossible to tell when he's telling the truth and when he's making stuff up. The reason this theory has gained momentum is down to what Eugene told Negan this past season: the same damn thing. He worked at the Human Genome Project weaponizing diseases as a way to fight other military forces.
Eugene acts like he's not exactly the sharpest tool in the shed. But when you think about it, what he's accomplished reeks of a science background - he made bullets and a poison pill. The way he talks about his "fake backstory" has a ring of authenticity to it. It's detailed and in-depth. So what if he really was involved with the creation of the virus and it's his fault that it was unleashed? While he was telling the truth that he doesn't know of a cure, he's not coughed up the biggest truth yet: that everything that's happening is completely his fault.
13. The apocalypse will end as soon as the zombies decay
What it means: According to this theory all that Rick's gang need to do in order to survive the outbreak is very simple. Stay put.
Birthed off the back of comments given by the show's FX guru Greg Nicotero -- that each season he pushes forward the decay of the zombies -- this idea is steeped in the science of how fast a body decomposes. Apparently time on the show since the outbreak began is approximately 500 days and so a year-and-a-half worth of decay by cadavers above ground matches Nicotero's zombie effects.
In order for a human body in those same conditions to completely disintegrate it should take two or three years. This theory supposes that for all living humans to survive they just need to hunker down for about 18 months or so to wait out the main 'tide' of walkers, then pick off those who turned post-outbreak as and when they encounter them.
14. The show is being told by Old Man Carl
What it means: Rick's a troubled hero. He's more beards than a hipster convention, and dodged a gajillion bullets, wire-wrapped baseball bats and the hungry, gnashing teeth of thousands of walkers. Why is he the centre of attention? What makes Mr. Grimes so darn special? Simple: because Carl idolises his father and it's Carl who's telling the entire story of the show.
The series will end with a major time skip where we see a much older Carl, with an eyepatch, recanting the story of how he grew up in the zombie apocalypse to someone offscreen. As he wraps up his tale, a walker shuffles nearby. "It's time go Judith," he says, as the camera pulls to back to reveal the young woman he's been talking to - his teenage sister wearing Rick's old Sheriff hat. She slays the zombie and the pair trot off into the distance.
15. It's a Breaking Bad sequel
What it means: Way back in season two it was revealed that Daryl had in his possession a bag of Merle's stuff when he rummages around in it for something to help T-Dog. Eagle-eyed viewers spotted his brother's stash of crystal meth at the bottom. And it's blue.
Fans of AMC's Breaking Bad put two and two together as Walter White's legendary cook-offs resulted in his signature blue brand of meth. This would suggest that The Walking Dead follows on from the events of that show, with Merle having purchased his ice from Walt or one of his various runners. Seeing as both are owned by the same network it's not too much of a stretch.
And further evidence emerged in season 5 when Daryl had a heart-to-heart with Beth, telling her about his dealer. Describing him as a "janky little white guy" he goes on to say that he once dished out a threat: "He says, 'I'm gonna kill you, bitch'." Sounds remarkably like one Jesse Pinkman.
16. Rick and Carl are zombies
What it means: Really? Granted, this is one of the more far-fetched ideas, along the same lines of "Rick's in a coma", but it's still worth considering. The whole thing is explained by suggesting that Rick and his son Carl are both immune to the effects of the virus. Much like any real-life outbreak not everyone falls victim or displays the symptoms of particular viruses when they take hold.
Over at Reddit one fan implies that Rick dies repeatedly throughout the show -- probably multiple times before we meet him, and once during the start of season 5 when Carl nearly ices him - because the way his body's biology responds to the infection is to mutate. It's so far gone that whenever he dies he doesn't return as a zombie, he simply returns to life. He can never die.