What makes Song's unusual punishment a "masterstroke"? Through years of such difficult confinement, how does she maintain her freedom?

At novel's end, the reader learns that Song is imprisoned for some time, denounced as a spy. In her cell, Song endures an unusual punishment: "I may lie only on my left side. I must always face the door, my hands visible. There is a paradise on my right side, a place of singing angels, and I dream of it every night. Even Thomas waits for me there. But I may not turn" (272). What makes this punishment a "masterstroke"? Through years of such difficult confinement, how does Song maintain her freedom?

Having done a little more reading, the unusual punishment of being confined in a small cell and allowed to recline only on one side was not an unknown rule of imprisonment. Song maintains her freedom by through her strong intellect, memories and independent thought. Her body was present and confined as her mind roamed free to improvise as the notes of jazz.