Why would the American government be interested in poisoning its population by spraying vapor out of an airplane? That remains unclear.

A couple of months ago, a video titled "Busted: Pilot Forgets to Turn Off CHEMTRAILS Before Landing" was uploaded to YouTube. (The version seen here is not the original upload, which was later removed with copyright claims.) Because the original was taken down, the exact view count isn't known, but it accumulated enough interest to be given the (admittedly nebulous) label "viral video" by Discovery News. Certainly, for a short and low-quality YouTube video about chemtrails, it was unusually popular.

The video is 40 seconds long, the first five of which are unintelligible. It quickly becomes clear (well, hazily clear) that we're seeing footage of an airplane coming in low for a landing at night. Trailing behind it are several stripes of aircraft exhaust. The plane passes a few lampposts, and by the 25-second mark, it's safely on the ground. At that point, the camera's operator zooms out and shifts left and up, panning over a stream of condensation left in the sky.

To most, this condensation would seem to be a pretty standard byproduct of flying in what look to be fairly foggy conditions. Hot airplane exhaust mixes with the lower-temperature atmosphere around it, and in the process, creates water vapor.

(I should add that I did not know exactly how to describe that process off the top of my head. I read about it on the Internet, and it made sense to me, so I'm repeating it here.)

But to the person who posted it, these 40 seconds show something much more sinister. It's not that he or she does not believe that the meeting of hot and cold air produces moisture, or that (though I wouldn't want to take words out of his or her mouth) every airplane that emits exhaust is up to no good. No, it's that real condensation shouldn't hang around so long, and that some airplanes are releasing a lot more than hot air.

THE BIRTH OF THE chemtrail conspiracy (the word "chemtrail" being a combination of chemical and contrail, and the word "contrail" a combination of condensation and trail) is generally pinpointed to a few-year window surrounding 1996. It was that year when the U.S. Air Force was first accused of using military aircraft to "spray" American citizens with mysterious substances, evidenced by the unusual contrail patterns left in the sky.

The third-best way to fan the flames of a conspiracy is to say you were only speaking hypothetically. The second-best way is to say, unequivocally, that any given practice isn't government policy. And the first-best way is to then say you've investigated people's concerns, and found them to be untrue

Probably not coincidentally, 1996 was also the year that a report called "Weather as a Force Multiplier: Owning the Weather in 2025" was presented (and made public) by students of the Air University. As an assignment, the Air Force chief of staff asked the study's authors to "examine the concepts, capabilities, and technologies the United States will require to remain the dominant air and space force in the future."

Though the paper's introduction clearly specifies that it does not reflect official government policy, and that the weather modification and control scenarios described within it are "fictional representations of future situations/scenarios," some took it as evidence that the government was actively working to control and manipulate the Earth's climate.

Unfortunately for the Air Force, the third-best way to fan the flames of a conspiracy is to say you were only speaking hypothetically. The second-best way is to say, unequivocally, that any given practice isn't government policy. And the first-best way is to then say you've investigated people's concerns, and found them to be untrue—which the Air Force did in 2002. And in 2005.

In the years since, the chemtrail conspiracy has spawned dozens of semi-activist websites and forums, like Aircrap.org and Chemtrails911.com. Most recently, many have latched on to this summer's Snowpiercer, a movie in which the government sprays chemicals into the sky in order to stop global warming, but instead "accidentally" creates a new ice age, killing everyone except a select few who are on board a perpetually moving train. The allegations from chemtrail activists are both broad and vague—it's not particularly clear why the United States government would be poisoning its own people, for example, and, if they were, why they wouldn't use a method more effective than spraying something in our general direction from 35,000 feet and hoping for the best—but one common, predominant thread is that chemtrails are making us sick.

One of the symptoms often said to be caused by chemtrails is very gross, and odd, and I'm sorry to write it here because upon reading you'll almost certainly feel like it's happening to you too: Many people who believe they've been infected by chemtrails also begin to believe that small, thread-like fibers are crawling out of their skin.

MORGELLONS DISEASE IS PROBABLY not a real disease. At least not in the way its sufferers think of it. It's a strange name, in that it's used both by people who believe they have it, and by people who say that believing they have it is all that it is. Many (if not most; though likely most) doctors and scientists consider it a form of delusional parasitosis, a kind of psychosis in which patients believe they're infested by parasites or other organisms that are not actually present.

Pressured by an Internet-based community of supporters (started by a mother who diagnosed her two-year-old son with the condition), the Centers for Disease Control and Prevention undertook an investigation into the supposed disease, publishing its results in 2012. Researchers found no "causative medical condition" or infectious agent, and they instead attributed patients' symptoms to delusional parasitosis. (Some of the patients likely had other potential contributing factors—50 percent tested positive for drugs.)

Still, several swaths of the Internet continue to reference the disease—and the health threat presented by so-called chemtrails in general—in earnest. This page even presents preventive dietary recommendations and a recipe for something called "Spring Hepatic Detox" tea, which the author writes is "Good to do, if you have been tested for heavy metals."

Many of these sites' authors and forum contributors post pictures of themselves taken from microscope slides: pieces of skin and specks and fibers, all thread-y looking and strange-colored, the way all hyper-zoomed in images of things are. I could look at them forever (not that I'm volunteering—this is a hypothetical), but it wouldn't make a difference. That's all a conspiracy theory really needs, isn't it? I admit, I like them for their reliability: Two opposing teams looking at the exact same thing, each convinced the other is missing it for what it really is.