graffes hum at night to keep their herds together.

 rattlesnakes can change the frequency of their distinctive rattle to create the illusion that they are much closer than is actually the case. they do this to frighten off predators.

disney's animated film, fantasia, was the first film with stereo sound.

a team of scientists from mit have discovered how to tell what you said by watching the vobrations of a bag of chips that was near you while you said it.

baby rats laugh when tickled, but it's ultrasonic, so only other rats hear it.

because there's no atmosphere in space, there's also no sound (sorry, star wars and guardians of the galaxy fans - all explosions are silent).

also, because mars has a thinner atmosphere than we do, with a different chemical makeup, sounds are higher-pitched there.

blue whales sing, and all of their singing voices have steadily dropped in pitch over at least the last 40 years. no one knows why.

you have amazing hearing. want proof? if there are no other sounds present, you can hear a piece of chalk dropped up to 10 miles away.

(what's chalk?)

an insect called a water boatman is the loudest creature in the world, relative to its size: more than 99 decibels (as loud as a full orchestra). and it makes all of this racket with its penis.

elephants communicate over hundreds of miles by making sounds too low for the human ear. the sound travels through the ground is picked up by other elephants via pads in their feet.

a blue whale's heart is roughly the size of a volkswagen beetle. it can be heard beating up to 2 miles away.

contrary to what you may have heard, a duck's quack does echo.

a lion's roar can be heard more than 5 miles away.

you can only hear about 1% of the entire audio spectrum. for all practical purposes, human beings are essentially deaf.

naturally-occurring sounds below 20hz (the lower level of human hearing) can cause people to hallucinate and/or experience feelings of intense fear, awe, or revulsion. it is believed that ghost 'sightings' and other supernatural phenomena are likely caused by sounds in this range. the study of such sounds is called infrasonics.