Certain sounds can be used as weapons. The U.S. Army has developed a "sonic bullet" that projects a narrow beam of high-powered sound, capable of stopping a person in his tracks with a major migraine. Annoying sounds, like a baby crying, can render an enemy useless immediately, and for as long as the sound is playing. The minute the speaker is switched off, the associated pain ends. Also related are beams of sound that can be used for targeted advertising - say you're walking past a Coke machine and you hear someone pouring a soda over ice.

Different natural phenomena can contain particular sound frequencies that can cause upset, sometimes subliminally. The Chinook and Foehn winds may resonate at a frequency that can cause irritability and migraines in humans. Infrasound may be upsetting to animals, who commonly exhibit strange behavior before an earthquake. Some people have reported feelings of anxiety and even physical symptoms (like incontinence) during the migration season of whales, which use infrasound to communicate with each other over distances of 10 miles or more. Some people even claim that certain meditative chants are what cause them to go into deeply introspective states.

There are even different towns around the world that suffer from a "hum" - a low noise that only certain people can hear, who can be greatly affected by the noise. Some people end up having to move away from town due to headaches, dizziness, and nausea. Infrasound can also cause anxiety, chills, and sorrow, and has been shown to snuff out candles. Keep that in mind the next time you visit a haunted house.

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