This poem describes two children, a brother and sister, cruelly killing butterflies on a Sunday with a common pin. The girl shrieks as she eviscerates the abdomen of one butterfly. The narrator reflects on the "heredity of cruelty everywhere" and how even innocent summer dresses can be torn. The mind fears seeing normal signs that could foreshadow future grief or violence. Overall it shows the darkness that can lurk beneath innocent childhood games and a seemingly idyllic summer day.