It doesn’t seem particularly fair that, with everything else to worry about, any of us could die at any moment from not much more than a feeling. That’s an oversimplification, but it’s technically true. While very unlikely, it is possible that, even considering a person with otherwise perfect health, something terrifying could come along, jolt her insides, and kill her.

Presumably, in cases like these, the medical examiners don’t put “terror” down for cause of death on the death certificate. In whatever examples scientists have considered to be proof of humans’ capacity to die of fright, some variation on a heart attack always claims medical responsibility and ends the process. But the idea that fear could have started it—that you could, in theory, say to someone, as hyperbole, “You’re going to scare me to death,” and then, maybe, later it could end up coming true—is, uh, scary. (In a way, though, I suppose it is also vindicating, at least for the risk- and adrenaline-averse. You were right. You don’t have to go to any horror movies if you don’t want.)

While very unlikely, it is possible that, even considering a person with otherwise perfect health, something terrifying could come along, jolt her insides, and kill her.

It’s not news that psychological stress affects the heart. Although it was surprising, at least to me, that the colloquial term for typically treatable medical events like these is “broken heart syndrome,” and is labeled as such even on the Mayo Clinic website, where the following sentence, read in another context, could provide tidy reassurance for someone just getting out of a relationship: “The symptoms of broken heart syndrome are treatable, and the condition usually reverses itself in about a week.” But it has always been trickier to prove that stress itself could be the trigger responsible in select fatal heart attacks. It’s hard to be sure after the fact—especially if the deceased was alone at the time of death, or if no one has reason to wonder whether fear played a role—though not necessarily impossible, as some research shows that 3-D pictures taken of the heart after death can indicate whether or not stress played a role based on the shape of the heart and the blood vessels, which are blocked in typical heart attacks but are clear when stress is to blame.

It’s harder still to test whether dying of fright is possible ahead of time, because any laboratory experiment that proposed rounding up a group of young healthy people and attempting to scare at least some of them into sudden death—in an elaborate haunted house, maybe, or just by throwing them all into a pit of snakes and spiders—would likely be frowned upon. It’s the sort of outcome a researcher can’t really hope for. At least not openly.

I, PERSONALLY, AM NOT suggesting Dr. David Phillips derives any kind of macabre pleasure from unexpected, fear-induced heart attacks, though one might reasonably wonder after learning that his landmark study labeled the phenomenon “the Baskerville effect,” after the Sherlock Holmes novel The Hound of the Baskervilles, in which a character called Sir Charles Baskerville is frightened to death by what he believes to be an enormous fire-breathing demon dog.

The study, titled "The Hound of the Baskervilles effect: A Natural Experiment on the Influence of Psychological Stress on the Timing of Death" and published in the British Medical Journal in 2001, purported to find a way around the aforementioned ethical and logistical difficulties by relying on nature to set up control and experimental groups for the researchers. The control group was white people, who do not, as a group, hold any particular associations between the number four and death, while the experimental group was made up of Chinese and Japanese people. In Mandarin, Cantonese, and Japanese, the word for the number four sounds very similar to the word for death, and many of the people who speak these languages consider it unlucky. Some Chinese and Japanese buildings don’t list floors or rooms numbered “four,” and many people report feeling apprehensive and stressed about that day each month.

The study’s subjects were the 209,908 Chinese and Japanese Americans (as experiment) and 47,328,762 white Americans (as control) whose electronic death certificates were recorded between January 1, 1973, and December 31, 1998. Researchers used mortality rates to estimate an average expected mortality level for the fourth day of the month (which, in theory, should be the same as day three or day six) and then compared the actual mortality levels, for both groups of people, to that expectation.

The hypothesis was that the mortality rates of the experimental group should show peaks on the fourth day of the month, because the Chinese and Japanese, undergoing psychological stress on that day in particular, would be more likely to suffer sudden and fatal heart attacks on the fourth than on any other day. And the results confirmed it: on the fourth day of the month, on the whole, cardiac deaths for Chinese and Japanese were 7.3 percent likelier than average. When confining the sample to the state of California—where there are large populations of Chinese and Japanese, and where, therefore, cultural beliefs are likely to hold more power—that peak jumps to an astonishing 27 percent higher than expected. There was no observed significant difference for whites, and a number of alternative theories (like potential diet changes, refusal of medication, alcohol consumption, etc.) were discussed and ruled out. It had to be—at least in part, at least from everything they could tell, anyway—fright.

The “fourth-day peak,” as the researchers call it, did, however, occur only in patients with pre-existing heart conditions. This caveat doesn’t invalidate the results—the Chinese and Japanese subjects who were more likely to die of a heart attack were still observed to be even more likely to die on a certain day, in a frequency unmatched by the control group—but it does temper the cause for alarm. It’s an unlikely event for someone with a heart condition, and even more so for someone without one.

Still, it’s spooky, especially for anyone prone to generalized anxiety as a rule and occasional anxiety about unlikely, unpredictable, she-never-saw-it-coming-and-then-suddenly-she-was-dead freak medical events in particular. It’s almost enough to make you want to curl up on the floor, away from anything frightening, for the foreseeable future. But that also sounds like a recipe for boredom, another of those feelings we’re prone to exaggerating about. And in case you’re wondering, yes, you can die from that, too.