The piano has changed a lot over the years, just like the music written for it. But the most significant changes took place in the twentieth century, when people like John Cage and his contemporaries began experimenting with "prepared" piano. This is a technique where paper, felt, string, wire, pencils, etc. are placed inside the piano, usually between or among the strings. It gives the piano a different sound when certain keys are struck. And then, of course, you can always play the strings themselves, as you would on a harp.

Check out this unusual video to see just how this "preparation" affects the sound and gives the instrument a whole new dimension.