The symbol of the mockingbird appeared once again in this chapter. Explain

In Chapter 25, Jem and Scout are about to go to sleep on their cots on the back porch. Scout sees a roly-poly bug and goes to kill it. Jem stops her, saying the bug never did anything to harm her. Scout heeds his request and carefully takes the bug outside, noting internally that if anything, Jem is becoming more like a lady than she is. As she returns to her cot, she thinks of Dill and remembers his story of the day Tom Robinson died in late August.