Here’s something to try out next Halloween season. From The Original Ghostbuster:
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.
Erin Anderson
Tandy, a skeptical engineer, methodically investigated these and other strange occurrences at the haunted lab. He didn’t find any real ghosts, but in the process he discovered how you can manufacture ghostly experiences through sound.
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.
Erin Anderson
You won’t be able to hear the sine wave in this embedded video, it’s below the range of our hearing. Try putting it on in the background and see if it induces ghostly experiences for you.
Quirks and Curiosities 