While taking a walk in the city, you hear an astounding melody. Awed by the beautiful sound of the music, you look around and see a lonely woman sitting on the side of the street playing an instrument. Usually, you don't pay much mind to buskers, but this woman's mastery of her instrument piqued your interest very much. And what intrigued you even more is that she was blindfolded.

How could someone play an instrument while blindfolded?

Curious, you decide to walk over and watch.