Through a process of elimination Tandy found the experiences seemed to be caused by a fan in the lab which was producing sound in a frequency well below the range of the human ear. Armed with this result Tandy first ‘exorcised’ the ghost by having the fan removed, then later, having identified the exact frequency, reproduced the effect of the fan in experimental subjects. Intrigued, Tandy suggested the frequency must be resonating somehow with the body, causing a physiological reaction that manifested as apprehension, fear and the sense of other presences nearby, speculating further that since the effect could be reproduced it was at least possible that many supernatural experiences were the result of natural phenomena such as the wind blowing across open chimneys or pipes vibrating underground.
Many so-called supernatural experiences may well have natural causes, but it does not follow that all of them do. Similar effects can often be achieved by various means.You could, for instance, also say that supernatural experiences are characterized by the presence of low-frequency sounds.