To Kill a Mockingbird is not just a simple story of growing up. This book contains metaphors and symbolism that greatly increase its literary value.
Mockingbird
The most important symbol in this story is probably the mockingbird. The theme of the mockingbird is shown in the title and throughout the rest of the book. After Scout and Jem received air rifles for Christmas, their father Atticus said to them "Shoot all the bluejays you want, if you can him 'em, but remember it's a sin to kill a mockingbird."(p.129) Later, Miss Maudie explains that "Mockingbirds don't do one thing but make music for us to enjoy."(p.129) Here we learn that the mockingbird is a harmless and pleasant creature. In the story, the mockingbird symbolizes two people: Arthur "Boo" Radley and Tom Robinson. Both are discriminated against in Maycomb, when they are, in fact, gentle and kind people.
People referred to Boo as "a malevolent phantom" and that "any stealthy small crimes committed in Maycomb were his work."(p.11) This hatred began as fear because the Radleys were people who kept to themselves, and this act was "a predilection unforgivable in Maycomb"(p.13) In the end of the story, our opinion of Boo is changed completely as Scout overcomes her fear and discovers that Boo was really just a big child.
Tom Robinson, on the other hand, was discriminated against because he was black. Even though it was clear that he was wrongfully accused, the jury could not vote in favour of a black man over two whites. "And so a quiet, respectable, humble Negro who had the unmitigated temerity to 'fell sorry' for a white woman has had to put his word against two white people's."(p.295)
Lee uses the mockingbird frequently in the book, and with it reveals the sins of prejudice that exists among people.
Cemented Knot-hole
In a knot-hole of an oak tree at the edge of the Radley property was where the Finch children often received gifts from Boo Radley. Scout and Jem had found many surprises in it including gum, pennies, and an old spelling bee medal. In return, the children decided to write a short thank-you letter to him, and placed it inside the knot-hole. The next day, someone had filled it with cement.
This was the work of Mr. Nathan Radley, the brother of Boo. "Tree's dying" was what Nathan Radley told Jem. "You plug 'em with cement when they're sick."(p.89) But according to Atticus, "the leaves, they're all green and full" and "that tree's as healthy as you are, Jem"(p.90) Nathan had probably discovered Boo's activities, so he decided to fill the knot-hole with cement to stop him.
This act symbolizes the alienation and miscommunication that results in misunderstanding. This applies especially to that of the Radleys from the rest of Maycomb County. Before the rumours started, the Radleys were discriminated against because they "kept to themselves...they did not go to church, Maycomb's principal recreation, but worshipped at home; Mrs. Radley seldom if ever crossed the street for a mid-morning coffee break with her neighbors, and certainly never joined a missionary circle."(p.12) After Arthur joined a gang as a teenager, Arthur was locked inside the house instead of being sent to a boarding school by his father to avoid embarrassment to the family. Because of the Radleys' isolated ways, they were unknown to the townspeople, and were often the topic of spiteful gossip.
After his father had died, his brother Nathan became in charge. Because he was locked away for thirty years, Arthur had suffered more than mental damage. He was robbed of his childhood and his future.
Snowman
It was the first snowstorm in Maycomb County since 1885. Because there was only "a feeble layer of soggy snow"(p.92), Jem and Scout had to find other materials to help build a snowman. With earth, Jem built the structure of the snowman. But who has ever heard of a snowman built with soil? Jem then "scooped up some snow and began plastering it on"(p.95)
The snowman, though not as significant as the mockingbird, symbolizes the fact that the only way for humans to succeed in building civilization is for its races to work together. The dark earth represents black people, as Scout calls it a "nigger snowman"(p.94), and the snow symbolizes white people, with which the creation "gradually...turned white"(p.95). Without snow, the snowman just would not be true to its name, and without earth, it would probably be a puny clump of snow.
Mad Dog
"Tim Johnson was a liver-colored bird dog, the pet of Maycomb."(p.132) One day in February, as Jem and Scout went exploring with their air-rifles, they found Tim Johnson walking erratically but steadily towards them. Immediately, their housekeeper Calpurnia had informed the rest of the neighborhood. Eventually, Atticus shot him down.
This dog is the symbol of the madness and prejudice of the South in the 1930s. It had not "galloped, leaped, and lunged at throats"(p.135), but was a slow, steady malice that invaded the streets. According to Heck Tate, the sheriff, mad dogs "usually go in a straight line"(p.135). This symbolizes the stubborn attitude of the people of Maycomb, who were either too proud or too lazy to change their minds.
Tim Johnson was probably infected with a contagious disease, such as rabies, and so "he's just as dangerous dead as alive."(p.139) Here, Atticus was the hero who destroys the evil, and stops the disease of prejudice from spreading further.
Flowers
Scout and Jem hated Mrs. Dubose. "If she was on the porch when we passed, we would be raked by her wrathful gaze, subjected to ruthless interrogation regarding our behavior, and given a melancholy prediction on what we would amount to when we grew up, which was always nothing."(p.142) One afternoon, in a fit of rage, Jem used Scout's new twirling baton and flailed off all the tops off Mrs. Dubose's flower bushes. He was, of course, later punished by Atticus to read to the old woman every afternoon.
Some of the flowers that Jem managed to cut were camellias and snow-on-the-mountains. The camellia is the state flower of Alabama, and the act of cutting the flowers symbolizes Jem trying to destroy the prejudice of the people of Alabama, or people in general. But this was not, and will never, be a simple task. As Mrs. Dubose puts it, "Thought you could kill my Snow-on-the-Mountain, did you? ...the top's growing back out. Next time you'll know how to do it right, won't you? You'll pull it up by the roots, won't you?" This shows that in order to fight injustice we have to tackle the root of the problem, which was the attitudes planted in the minds of people for many generations. Pulling roots is far harder than cutting tops, which symbolizes the difficulty of destroying prejudice.