Imagine that you are a human being born on Earth who possesses the senses of sight, smell, hearing, touch, and taste. Imagine that you were kidnapped by a hexapedal alien civilization that had no sense of hearing, and these aliens produced loud screeches when they walked, the said screeches originating from a series of gills located on their squiddish lower appendages, which vented shrieks of hot gas whenever they processed calories to move. Every time one of them walked close to you, you were hit with sound waves so powerful that you clutched your ears in pain and fell to the floor. You developed headaches. Alien doctors determined that you were clearly insane, for feeling the presence of something that was not there.
Despite their inability to hear, they were a brilliant race. Within weeks they had adjusted their advanced visual computer programs to translate the movements of your mouth into their native sign language, and you became able to talk to them. Using their computer-aided translators as a medium, you pleaded with them that things called "sound waves" existed, and that they didn't know how to monitor them simply because their culture--though it possessed advanced spaceflight capability--had never learned about sound.
In time, when you were permitted to walk outside, you learned that this species had arisen from a planet with a core of compressed nitrogen, which slipped into the atmosphere hundreds of times each minute, only to be sucked back inside, producing an endless cacophony everywhere outside. Very few organisms on this planet have evolved hearing organs, as such a development would have precluded higher thinking functions and/or survival. Occasionally babies are born who never stop twitching, experience terrible pain, and die of unknown neurological causes in a matter of weeks; the planet's healers call this phenomenon "Random Expiration of Babies," or "R.E.B.," and devote the bulk of their money and attention to other, newer diseases.
One unorthodox alien scientist, convinced that you might be onto something, makes you some earphones, trusting that this will diminish your pain. It does, although by then, you have lost much of your hearing anyway, due to the constant barrage of noise. This scientist tries to work with you to better understand the nature of this supernatural concept known as "sound." Everyone else feels that she is crazy and irrational, but she persists. Your friend studies your ears, taking a number of highly detailed internal photographs, and presents her findings to her colleagues, suggesting that these insensible genetic dead-ends might have something to do with visualizing a different spectrum of light, which your culture might have deified as a demigod known as "sound." Her colleagues lambast her with examples of other useless or marginally useless organs found in their own bodies, including many misunderstood portions of their two-part brains, and suggest that your "E-A-R-S" are similar to many of the "dark regions" that characterize their own neurology. When your friend persists in pursuing her radically irrational supernatural fantasies, she loses her license, and is no longer granted access to the giant hospital where you are being stored along with test subjects from other planets.
Who's crazy now?