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In the early 1980s, a certain Mr. Vic Tandy found himself working for a medical device manufacturer in Warwick, in the county of Warwickshire, England. With a background in engineering, Tandy had been hired to work on medical devices in a slapdash laboratory that consisted of two steel garages connected by a series of ducts. Aside from the constant buzz of fans and pumps from the equipment, Tandy and his colleagues found little out of the ordinary about their workplace. Nothing, that is, until the apparition appeared.

Early one morning, Tandy arrived at the lab and found a terrified cleaning woman running from the premises. She was unable to explain what exactly had happened, apart from an overwhelming sense of dread and the feeling that she was distinctly not alone. Tandy chalked it up to her having worked the night shift isolated in a creaky old building. But in the following days, Tandy and his two equally hard-nosed and skeptical lab mates noticed an odd, unsettled atmosphere associated with their workspace. Tandy described it as a “depressed” feeling, and complained of breaking out into cold sweats. And there were other odd occurrences⁠—in one instance, a fellow was working at a workbench and felt someone watching over his shoulder, but when he turned to address them there was no one present. On another occasion, while Tandy was working alone, he became convinced that a gray, indistinct apparition was waxing at the edges of his vision, but he swiveled his head only to find that the thing, whatever it had been, had vanished. Tandy and his colleagues assumed these feelings must be due to exhaustion.

One subsequent day, Tandy was using the lab’s vice to perform some maintenance on his fencing foil, its handle locked in the jaws and its blade protruding outward. Tandy stepped away for a few moments and returned to find the blade bouncing violently up and down, compelled by an unseen force. Tandy snatched the foil and the vice together off the workbench, and the oscillations stopped. He placed the configuration back on the surface and, within moments, the blade began moving again. He walked the combination around his lab, and noticed that the blade remained still near the edges of the room, but the oscillations grew as he moved toward the center. The most violent movements occurred next to the workbench⁠—right where he had previously thought he’d seen a gray, indistinct figure.

A consummate engineer, Tandy concluded that there must be a standing wave of air in the room, causing the foil to move and, oddly enough, causing Tandy and his colleagues perceive a human presence. Investigating this hypothesis, Tandy found that a new exhaust fan had recently been installed. Its installation coincided exactly with the terror-stricken cleaning woman. Apparently the combination of the fan and the geometry of the room had produced a standing sound wave at a frequency of just under 19 Hz. This frequency, part of a region of frequencies dubbed infrasound, is just out of the range of normal human hearing, but is very close to the average resonant frequency of a human eyeball. This caused the lab workers’ eyes to vibrate very slightly, prompting the curious optical illusions. When the fan was replaced, the apparition vanished for good and the lab returned to normal, non-spooky operations.

Infrasound is thought to be responsible for similar phenomena in other contexts, such as organ pipes inadvertently creating low frequency sound waves and feelings of a ghostly presence. Tandy’s observations in the medical device lab eventually led to the publication of brief scientific paper on the phenomenon, and Tandy parlayed his accidental expertise into a quiet but continuous dedication to debunking paranormal claims until his death in 2005.