The answer is: "Yet Gregor's sister was playing so beautifully. Her face was leant to one side, following the lines of music with a careful and melancholy expression. Gregor crawled a little further forward, keeping his head close to the ground so that he could meet her eyes if the chance came. Was he an animal if music could captivate him so? It seemed to him that he was being shown the way to the unknown nourishment he had been yearning for. He was determined to make his way forward to his sister and tug at her skirt to show her she might come into his room with her violin, as no-one appreciated her playing here as much as he would."
In Kafka´s novella, Gregor Samsa finds himself turned into a bug. He eventually undergoes a mental transformation that starts to match his bodily condition, but still, his thoughts and memories remain somewhat human, but different. His memories of food, for example, still arouse his appetite, but when he tries food for humans, it no longer tastes good. The same happens with his memories of movement and of rest. But there seems to be one thing that he can still appreciate fully in his new form just as much as he enjoyed it when human, his sister´s music and its beauty. In fact, the answer above shows a determining moment in the story as he leaves his room after being so moved by his sister´s music, and this event, which disgusts his family so much is enough to make them take the resolution to get rid of him.