The mob scene of To Kill a Mockingbird establishes both the historical context and the mob/herd mentality of human nature in Harper Lee's narrative. In an indictment of the social code of the South, Lee loosely bases her character of Tom Robinson upon that of Emmett Till, a black youth who in 1955 had allegedly harassed a white woman and, consequently, was killed as a result of a severe beating by white men. Under the Jim Crow Laws, all that was necessary was the accusation by the white against the black; no proof was required. So, since Mayella Ewell has made an accusation of rape by Robinson, the mob of Walter Cunningham, Sr., forms in a pre-conditioned act and drives into town to the jailhouse where Robinson is being kept. There, they demand that Atticus hand over Tom so they can take him and kill him. This intention of theirs reflects what was done in order to re-establish the fear of the white man and prevent other blacks from talking or interacting with white women.
That there is a mob mentality is exemplified by Scout's singling out of Mr. Cunningham. For, when she speaks to him individually, calling him by name,
"Hey, Mr. Cunningham. How's your entailment gettin' along?"
Mr. Cunningham feels singled out from the safety of the mob/herd, and he also begins to think on his own. As Scout innocently talks to him, Cunningham, who is essentially a decent person, recalls the kindnesses that Atticus Finch has shown him and is overcome with guilt that he would now join in the physical and mental intimidation of this kind lawyer. In a completely different state of mind, Cunningham then stoops to Scout and tells her he will give his son her message.
"Let's clear out...Let's get going, boys," he orders the others, and they depart as the psychology of the mob has been broken and their mindless act of hatred placed into its proper context.