What we don't hear

One sound I totally ignore but hear all the time is my computer mouse. And my keyboard. The muffled tapping of soft fingers on cushioned keys. How many sounds do I not hear every day? How much of the world do all of us miss because we have tuned out our immediate surroundings? Perhaps it is natural for the "normal" sounds to fade, so unusual sounds can catch our attention and raise the alarm. Then again, the sounds we hear everyday are actually quite dominant, even if we are not aware of it. They mask other sounds. Consider central air conditioning. If the air conditioning in your office building suddenly stopped, the "silence" would be deafening. If all of our computers, cell phones, coffee machines, refrigerators, fans, water heaters, radiators, escalators, elevators, garage doors and car motors suddenly stopped, all over the world, it would be an M. Night Shyamalan moment!