Atticus says to Scout, "Mr. Ewell fell on his knife. Can you possibly understand?" What was her response? Explain what she meant.

Scout understood that Arthur was like a mockingbird and they had to protect him,

I ran to him and hugged him and kissed him with all my might. “Yes sir, I understand,” I reassured him. “Mr. Tate was right.” Atticus disengaged himself and looked at me. “What do you mean?” “Well, it’d be sort of like shootin‘ a mockingbird, wouldn’t it?”