I was teaching this eleven year old girl how to play a piano piece and it required each of her hands to play different melodies. She was enjoying learning the piece and at one point had to struggle through a part that was complex precisely because of each hand playing something unique. It posed a problem; a short circuiting problem of exactly what it represented, doing two different things simultaneously. As she got closer and closer to accomplishing it, I watched different expressions come over her face. Then pointed out the execution of this type of piece stops one from thinking. She laughed the laugh of recognition. I said when you catch yourself thinking again, it falls apart, no? She laughed harder. All of Bach’s music seems like it has between 2 to 4 parts played simultaneously.