It seems that the word mockingbird only appears six times in this book. We first hear about mockingbirds in chapter 10. Jem and Scout receive air rifles for Christmas. Scout recalls that Atticus told Jem that he
would rather you shot at tin cans in the backyard. But I know you'll go after birds. Shoot all the blue jays you want, if you can hit them. But remember, it's a sin to kill a mockingbird.
Scout is struck by this. It is the only time that she can recall her father saying that anything is a sin. Miss Maudie explains what Atticus means when Scout asks her about it. She explains,
Mockingbirds don't do one thing but make music for us to enjoy. ... That's why it's a sin to kill a mockingbird.
Later in that chapter, a rabid dog wanders down the street. Everyone in the neighborhood locks their doors and stays inside for safety. Atticus arrives with the sheriff looking to put the dog down. Scout remarks,
Nothing is more deadly than a deserted waiting street. The trees were still. The mockingbirds...
(The entire section contains 3 answers and 813 words.)