Read this: Songbirds and their associated symbolism appear throughout the novel. The family's last name of Finch also shares Lee's mother's maiden name. The titular mockingbird is a key motif of this theme, which first appears when Atticus, having given his children air-rifles for Christmas, allows their Uncle Jack to teach them to shoot. Atticus warns them that, although they can "shoot all the bluejays they want", they must remember that "it's a sin to kill a mockingbird". Confused, Scout approaches her neighbor Miss Maudie, who explains that mockingbirds never harm other living creatures. She points out that mockingbirds simply provide pleasure with their songs, saying, "They don't do one thing but sing their hearts out for us." Writer Edwin Bruell summarized the symbolism when he wrote in 1964, "'To kill a mockingbird' is to kill that which is innocent and harmless—like Tom Robinson." Scholars have noted that Lee often returns to the mockingbird theme when trying to make a moral point.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): Which bird does Atticus Finch say is a "sin to kill?"
mockingbird