Normal sound occupies the frequency of about 20 vibrations a second (a vibration per second is a Hertz through to 20,000 Hertz. Frequencies beyond 20,000Hz are called ultrasound. Infrasound is the opposite; it's frequencies from about 1 Hz to 20 Hz.

Infrasound has many interesting properties. For starters, infrasound has longer range than sound. Animals that can hear infrasound, like elephants can use it easily over distances exceeding one kilometer to communicate with other elephants. Seagulls use infrasound generated by ocean waves to tell them which way the water is.

Another interesting feature is that the body cavity has a natural frequency of 3-7 Hertz. This means that if you are near an infrasound generator at this frequency, then your own internal organs will begin to resonate, which will at least make you feel very sick, and in one case caused haemorrhaging occasioning death. Your anal sphincter apparently also has a natural frequency of 10-15 Hz, and apparently there are a new wave of crowd control devices that vibrate in this range, causing people to want to defecate. These devices literally give you the shits.

A new study conducted by a pair of British scientists theorize that infrasound may be responsible for people's supernatural feelings. A pair of acoustic scientists at the National Physical Laboratory in England tested the impact of infrasound on 750 people at a concert by playing four pieces of music, some of which were laced with infrasound frequencies produced with a seven meter pipe.

The audience didn't know when the infrasound was inserted into the music but 22 percent of them reported feelings of sorrow, chills down the spine, nervousness, revulsion or fear during the infrasound-laced pieces.

"These results suggest that low frequency sound can cause people to have unusual experiences even though they cannot consciously detect infrasound," said one of the scientists who performed the experiment suggesting that people's feelings of ghosts, spirits or other supernatural phenomenon may be linked to or caused by occurrences of infrasound.

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