Cars is a charming, funny, well-crafted Pixar animated classic released in 2006. It was Pixar's last independently produced project before being bought by Disney entirely and has generated a staggering number of dark, macabre fan theories that run the gamut from genocidal annihilation to David Cronenberg-esque body horror.
The film - set in a world resembling modern-day Earth but populated by anthropomorphic vehicles - tells the story of a hotshot rookie race car who stumbles upon the small, rural town of Radiator Springs after getting lost on the way to the biggest race of his life. Through forming new friendships with different types of other cars, each with their own lives and rich personalities, he learns the importance of friendship and humility. So it only makes sense that fans looked at that premise and thought, "Okay, but how can I make this give people nightmares?"
Cars was followed by two sequels - the creatively named Cars 2 and Cars 3 - as well as several "non-canonical" spin-offs, including the 2013 film Planes, it's direct-to-DVD sequel Planes: Fire & Rescue, and multiple Disney Channel cartoon TV shows. Each one of these expansions to the universe - which is noticeably devoid of humans despite many, many indications of their past existence - have only added fuel to some truly disturbing entries in the genre of Disney-Pixar fan theories.
While it's easy to get wrapped up in the anthropomorphising of the cars and accept their human qualities - like Fillmore the VW Bus acting like a stoned hippy, implying there are car drugs - some of these funny world building moments suggest some truly bizarre aspects and implications for the society in Cars.
Namely, as pointed out by Redditor u/Jru247, Cars 2 raises serious questions about the presence of organized religion among the sentient vehicles: "In Cars 2 we see the popemobile. There's a car papacy? Is there Cartholocism? Was there a St. Peter car, or a Jesus Chrysler? Are there other religions?"
Tumblr user calumnw goes further, pointing out the ramifications of this throw-away joke: "The pope is a car in a pope hat. He rides around in a Popemobile. A CAR is riding in another car. they make reference to the Popemobile. 'Is the Popemobile Catholic?'... presumably this means the Popemobile is employed and must be specifically Catholic in order to be the chauffeur and carrier to the regular pope. Also, Catholicism is in this universe! This means that there must have been an actual Jesus Christ car."
Some fans seem to think that the creators of Cars 3 essentially erased Cars 2 within the universe of the franchise.
According to Redditor u/Gravitysilence, based on the trailer for Cars 3 and in-film evidence, it seems that Cars 3 was meant to be a hard reboot so-to-speak, that was meant to ignore the fact that Cars 2 ever happened - just like how the 2018 Halloween film was meant to be a direct sequel to the 1978 original.
In one of the trailers of Cars 3, we can hear Smokey speaking over the scene of McQueen crashing. Smokey says, "You can't turn back the clock, but you can wind it up again." The phrase was chosen intentionally by Pixar to let us know that Cars 3 was made as a franchise reset.
This can be backed up by the lack of anything from Cars 2 having effect on Cars 3. The events of Cars 2 are never mentioned in Cars 3, and lessons learned in Cars 2 now have to be relearned. Pixar probably wants to forget about the second movie and so has made Cars 3 with only the first movie's plot in mind.
In the Cars universe, humans don't exist - that's just generally accepted. If you look at the famous Jon Negroni Pixar Theory, which states that all Pixar movies share the same universe, it's argued that the Cars films take place after the human exodus that we see in WALL-E. However, The Film Theorists' MatPat adds onto that theory suggesting that the cars in Cars are actually "a highly evolved form of insect."
"It sounds ridiculous, but think about it! Just like an insect has a hard exoskeleton made of chitin, the creatures in the Cars universe have evolved a stronger exoskeleton made of various metals," MatPat explains. "An insect's exoskeleton isn't a single surface, but rather consists of multiple jointed plates, so that when an insect moves a muscle, it causes the connected exoskeleton plate pieces to move as well. It's the same style of movement that we see in the cars."
As further evidence, MatPat points to the fact that the cars appear to be organic - as they eat food and get the hiccups, among other things that would require a non-mechanical biology - as well as the fact that they can straight-up grow dragonfly-like wings and flitter around as actual insects. Just look at the Vroomaroundus Bugus, a literal VW beetle that is "usually indigenous to warm dry climates," and has a "relatively short life span," according to supplementary material on the Cars Blu-ray.
Sally - a 2002 Porsche 911 Carrera and small-town lawyer - came to Radiator Springs after leaving her old life as a high-powered litigator in Los Angeles behind her. According to a featurette on the Cars Blu-ray, "Sally grew tired of her life in the fast lane… and made a new start in the small town of Radiator Springs." The official Blu-ray extras also state, "Sally's tattoo pinstriping is left over from her early days. Though she's a little embarrassed by it now, it serves as a reminder of her high-speed life in California and how happy she is to be cruising in the slow lane."
However, what if she didn't actually intend to live in Radiator Springs at all? What if she became so overwhelmed or disillusioned with her "high-speed life" that she simply intended to drive off into some remote area and end it all? Redditor u/SolidBones thinks there's quite a bit of low-key evidence to suggest Sally ended up in the rural Route 66 town after she attempted to take her life.
When Lightning drives off with Sally to the [Wheel Well Motel], he asks her how a (likely rich) city Porsche ended up in nowheresville. She responds that she did indeed have a lavish life, "but [she] wasn't...happy,' with a far off look. This is a common sign of depression - not being able to find happiness even in situations where most others do. Then she says she drove away from home into the desert until she 'broke down.' Not ran out of gas, broke down. We know that cars [perish] in this universe, and I would suspect breaking down and crashing are the only ways that happens.
"Then she talks about how Mater found her and towed her back. She didn't call for a tow or anything - she was found, broken down, alone in the desert, driving away from her life without a destination… She's in love with the town because they saved her. She's 'one of them' because a bunch of older cars found a young car in distress and adopted her."