The poem, "Uncle's First Rabbit," recounts a young boy's first, terrifying experience with the act of killing another living thing. He has dreamed of this moment, a coming-of-age, a step towards adulthood, as he carefully aims the rifle. Then, shockingly, he is confronted with "the terrible singing" of the frightened rabbit.
Rabbits are pretty quiet animals, but they can make grunting noises when they are frightened, and when they are really in danger, they can scream. The screaming of the rabbit in this poem foreshadows the violence the boy's mother experiences at the hands of his drunken father. The mother, like the timid rabbit, "sings" when she is most scared.