Essentially, sound is a pressure wave that causes vibrations as it displaces and moves the air around it, which our ear drums pick up and our brains interpret. The human brain gathers and infers a LOT of information through sound because sound waves carry a lot of clues about the physical properties or events that created them. For example, if someone drops an object on the floor, the sound waves that come from the object striking the floor tell our brains about the kind of surface the object hit as well as the physical properties of the object—its approximate size, weight, material, and shape.