Similes are figurative expressions in which the author wishes to convey his or her perceptions to the reader and create an image in the reader's mind. The author draws a direct comparison between two seemingly different things by usually using the words 'like' or 'as'. This literary technique makes it easier for the reader to understand the writer's purpose and enables him/her to engage more effectively with the text.
In chapter one of To Kill a Mockingbird features a number of effective similes:
Ladies ... were like soft teacakes with frostings of sweat and sweet talcum.
Scout, in describing the heat and how the ladies of Maycomb coped with it, compares them to frosted teacakes. She suggests that they were gentle, sweet and harmless. One can therefore expect that they did not pose any danger or risk. This description contrasts sharply with what we learn of the women of Maycomb later.
In describing Dill, Scout later mentions that:
...we came to know Dill as a pocket Merlin...
In comparing Dill, Scout alludes to the famed and legendary wizard Merlin, an important character in the tales of King Arthur. She exaggerates by comparing Dill to the celebrated character but effectively portrays the fact that what Dill said and did enthralled her and Jem so much that he seemed almost magical. Dill was a smaller version of Merlin.
In a later discussion about the Radley house, Scout mentions the following about Dill:
...it drew him as the moon draws water.
In using this simile, Scout is describing Dill's overwhelming fascination with the Radley house. By comparing it to a natural event, she is suggesting that Dill's attraction is instinctive. He cannot control his desire to be close to the house. It is as if it draws him in, as the moon's gravity pulls on the oceans, creating tides. It is an irresistible and uncontrollable urge.
When they discuss Boo Radley, Scout refers to Miss Stephanie Crawford's description of him by using a simile:
...his head was like a skull lookin' at her.
Miss Crawford's portrayal supports the stereotypical view everyone in Maycomb had of Boo. He had become, in essence, the town's bogeyman. Boo was surrounded in mystery and theories about him abounded. He was perceived as a pernicious creature, out to do harm. The comparison to a skull adds to the mystery and horror associated with him. The death's head implies danger and something supernatural. Ironically, though, the children later discover that the town's perception of Boo could not have been further from the truth, for he is the one who rescues them from Bob Ewell's malice.