This is actually one of the more risque scenes in the very proper relationship between the widowed neighbors Atticus Finch and Miss Maudie Atkinson. Many readers must have wondered if the two old friends had ever considered getting together matrimonially since Maudie would have been a great mother for Scout and Jem. Maudie and Atticus's brother, Jack, have a joking relationship about marriage, but it only consists of Jack "trying to get Miss Maudie's goat," and Maudie responding in a teasing manner. This scene also shows a rare glimpse of Atticus's humor. When he came home from dinner one day, he found Scout "crouched down" with her air rifle in her hand. When Atticus asked what she was aiming at, Scout responded,
"Miss Maudie's rear end."
Atticus took a look at Scout's "generous target" and decided to warn her.
"Maudie," he called, " I thought I'd better warn you. You are in considerable peril."
Miss Maudie straightened up and looked toward me. She said, "Atticus, you are a devil from hell."
It was simply a joking response--and for Maudie, a somewhat off-color one--to an old friend whose tomboy daughter dared to take aim at Miss Maudie's inviting derriere.
In To Kill A Mockingbird, Miss Maudie is an important character who is instrumental in Scout's development. She is a sounding-board for those things that confuse or confound Scout and, despite her "acid" tongue she is a very likable character in a town where hypocrisy and a lack of self-awareness are the order of the day. Miss Maudie, like Atticus, knows that she cannot change the perspective of the townsfolk directly but she makes sure that she disassociates herself from their own contradictory behavior. An example of this is when in chapter 5 Miss Maudie talks about the "foot-washing baptists." She wants Scout to understand that she is a Baptist but that the foot-washers lack a critical understanding of life's aims, believing that "anything that's a pleasure is a sin." She is not false like so many in Maycomb County and refuses to conform which is why Scout has "considerable faith" in her.
By chapter 10, things are not going well for Tom's trial as "the only thing we've got is a Black man's word against the Ewells'" (chapter 9). It is Miss Maudie with whom Scout discusses the famous line "it's a sin to kill a Mockingbird" as she and Jem have been warned by their father not to use their air-rifles inappropriately. As Scout aims her air-rifle in Miss Maudie's direction, there is playful banter between Atticus and Miss Maudie. They do not feel the need to behave according to the expectations of the townsfolk and can joke with each other. As they both have a "dry" sense of humor, where jokes are told in a detached and seemingly dispassionate manner, they understand each other. The lack of apparent emotion reinforces their personalities and Miss Maudie means that Atticus is being cheeky and rather bold such as their friendship and understanding allows.