In November 2016, a U.S. diplomat who had recently arrived in Havana reported hearing a strange, high-pitched sound outside of his home, according to a ProPublica investigation. It was loud enough that he had to close his windows. He didn’t think too much of it; it didn’t make him initially feel ill. But over the following months, other diplomats reported the buglike noise too—you can listen to an AP recording here—along with earaches, hearing loss, headaches, nausea, and trouble sleeping. Many of the symptoms were like those of a concussion, but without any apparent blow to the head. Indeed, there was no clear cause.

In the time since, federal investigations, scientists, and many news outlets have attempted to surmise what caused these strange symptoms, which dozens of diplomats experienced over a year and a half in Cuba. It’s a mystery practically inviting conspiracy theories about spies wielding weaponry capable of destroying the human mind with invisible waves. Despite all of the efforts to solve it, there is no firm conclusion yet. There isn’t even a conclusion with the structural integrity of Jell-O. It might be years and many more papers until we know what happened for sure, if we ever do: Science is slow and iterative, quick to present ideas, and hesitant to crown a winner, and we are in the middle of watching it frustratingly play out. “Reaching a firm conclusion would likely require many more new cases, a situation that nobody is eager to see,” noted Benedict Carey in the New York Times this week, reporting on a new study comparing the brains of diplomats with a control group. That study essentially concluded, basically, “Yes, something happened. No idea what!”

The lack of clarity hasn’t stopped journalists from reporting on the ideas proposed by scientists and researchers and government officials, or from proposing ideas themselves. What might be to blame for the sonic attacks in Cuba? What follows is a look of the possibilities aired so far, ranked in highly unscientific order from least likely to most.

Noise

The first person to seek help for symptoms, in December 2016, noted that they occurred after hearing the strange noise; the first rumors were of “sonic attacks” and a “sonic weapon,” The New Yorker explains, which is probably why headlines still refer to them as “sonic attacks.” But the link probably doesn’t extend beyond either coincidence (though it’s possible the noise was a decoy). The sound’s relevance here has more do to the way we tell stories and connect information than with science. While the Pentagon itself has in the past tinkered with sonic weapons that could cause ear pain, according to Vanity Fair, these devices didn’t make it past the experimental phase. They were too bulky, and the noise would have had to be extraordinarily loud to do any damage—louder than what the diplomats reported hearing. Not a very stealth weapon, at any rate. Which is why, by January 2018, the FBI had ruled out a sonic weapon, according to ProPublica.

Microwaves

The New York Times declared this the top possible cause just last fall, pointing to an experiment from the 1960s that suggested that microwaves could be sometimes heard as sound, and some speculation from experts. But the Washington Post issued a fact-check of the science: Microwave radiation from a distance would be far too weak to make noise or cause damage, the Post argues, and the diplomats were not, as far as we know, strong-armed into kitchen jury-rigged appliances. “It would be a bad idea for you to stick your head inside a microwave oven while it’s on,” the Post helpfully clarified nonetheless, and also noted that those pushing the microwave idea cite studies looking at links between cellphones and cancer (also not a thing). Ultimately, those arguing microwaves were used in Havana are “not giving any evidence,” a physicist told the Post.

A Viral Infection

This has been floated a few times, but as one study points out, the affected diplomats lacked a common sign of a virus: a fever. And while viruses can affect the brain, there’s no evidence that they can produce the symptoms seen in the diplomats. But maybe this will lead to a new biological discovery. Who knows!

Previous Trauma

Maybe all of the complaints are the lingering result of past traumas that had previously gone unaddressed? Trauma is pretty poorly understood. But the authors of the recent JAMA study argue that the brains of the diplomats are similar enough to each other, and differ enough from a control group, to rule this out.

Crickets or Cicadas (Partially)

The recording of the sound the diplomats heard was identified by scientists as Indies short-tailed crickets, Carl Zimmer explained in the science section of the New York Times in January, covering a preprint of a study analyzing a recording of the sound the diplomats heard against field recordings of insects. It wasn’t a perfect match, though, perhaps because the recording was taken from indoors. While it seems likely this explains the sound itself (the scientists, and Zimmer’s piece, which consults an outside expert, are pretty confident), the crickets probably aren’t dangerous. As biologist Allen Sanborn, who at one point thought it might be cicadas, told ProPublica (and probably the FBI, which he consulted with), the noise from the insect “wouldn‘t really hurt you unless it was shoved into your ear canal.” The actual cause of harm was perhaps masked by the noise or, more likely, just an entirely different phenomenon altogether.

It’s All in Their Heads

We don’t mean this pejoratively: The brain abnormalities could be a striking example of the impact stress and social contagions can have on human bodies. “If your government comes and tells you, ‘You’re under attack. We have to rapidly get you out of there,’ and some people start feeling sick … there’s a possibility of psychological contagion,” Mitchell Valdés-Sosa, an expert working on the mystery for the Cuban government, told Sarah Kaplan and Joel Achenbach at the Washington Post.

Cuban scientists aren’t the only ones backing this idea. “Think of mass psychogenic illness as the placebo effect in reverse,” medical sociologist Robert Bartholomew told Jack Hitt at Vanity Fair. (That piece concludes that this explanation is the right one.) “You can often make yourself feel better by taking a sugar pill. You can also make yourself feel sick if you think you are becoming sick. Mass psychogenic illness involves the nervous system, and can mimic a variety of illnesses.” In Slate, Frank Bures further explained why “it’s in your head” isn’t synonymous with “it’s not real.”

And yet! Even though we know stress and anxiety can cause physical pain, it’s still unclear how they would cause the particular pain and the brain changes the diplomats appear to have experienced. And ultimately, this explanation feels somewhat unsatisfying. But sometimes, that’s the best you can do.