If there were ever a character created to fit the term "redneck," it would have to be Bob Ewell.  He eagerly takes the stand during the trial, and proceeds to answer questions with an arrogant demeanor.  He is clearly enjoying his "fifteen minutes of fame" and because he has accused a black man of raping his (Ewell's) white daughter, he is also enjoying the only situation he will ever be in where he will be "superior" to someone--because even though he is at the very bottom of the social strata, in the Deep South in the 1930's, he is superior to every black person he will encounter.  Ewell's festive demeanor vanishes when he figures out that Atticus is making him look foolish.  When Atticus proves that Bob Ewell was left-handed, and calls everyone's attention to the fact that Mayella's injuries were on the right side of her face, Ewell becomes angry and accuses Atticus of being dishonest and taking advantage of him.  Mayella is a slightly more sympathetic figure; Scout points out that despite the filth and squalor of the Ewell homestead, Mayella keeps several containers of beautiful geraniums along one side of the "yard".  Mayella is immediately wary of Atticus's questions, unlike her father, who seemed to be enjoying himself at first; Mayella is also much more aware of her position in Maycomb society, and becomes defensive toward Atticus more quickly than her father did.  She cries during much of her testimony and, clearly afraid of her father's abuse, shuts down when Atticus begins to discredit her story, making it ever more apparent that Ewell actually assaulted her, not Tom Robinson.