Reading "letter to his father" the reader better understand the metamorphosis by providing:

This thinning would materially change the sound of the drum, evidence that although it might continue to be used for its original purpose of music-making or calling people to arms, it would now do so with a different voice. a musical instrument had become a trophy, and the new carvings were in fact branding, a statement of the north’s political dominance over central africa and of allegiance to islam. the drum had come to khartoum at a critical moment in sudanese history. in an audio version, stressing the word "branding" would do what for the listener? emphasize the word's importance and the idea that followsadd emphasis to the following sentencesignal that something important has just been repeatedadd emphasis to the preceding sentence