The mob left because of the way Scout talked to Mr. Cunningham. People in mobs tend to act sort of crazy because they don't feel like they are individuals. Each person sort of forgets he's an individual with a conscience and loses himself in the crowd mentality. When Scout talks to Mr. Cunningham, she sort of breaks the spell.
The significance of Mayella's bruises is that they were probably inflicted by a left-handed person. Her dad is left handed and that sort of implies that maybe he's the one who hurt her.
To answer the second part of this question, if you punch someone's face with your left hand, it will hit the right side of their face. this proves Tom's innocence because his left hand is crippled.
When you are in a mob, you become a collective identity as a group fighting along the said ideology for different reasons. Thus, when Scout speaks, they suddenly lose focus of the agenda at hand and suddenly the spirit is gone.
You punch the right side of the face with your left hand and vice-versa. This would suggest that her father injured her.
Mr. Cunnigham's mob left because Scout interrupted and saw Mr. Cunnigham, she began talking to him about Walter Jr. Cunningham, his son. Mayella's bruises were on the left side of her face. This tells us that Tom is innocent because his left hand is crippled.
1. Each member of the mob's safety lay in anonymity. An action taken by a mob seems less reprehensible than the same action taken by an individual. When in a mob, each person is simply part of it, not singled out as an individual. When Scout talked to Mr. Cunningham, he was indentified as a family man, a father, not just a part of the mob. Personal dignity and integrity can be much more easily forgotten in a group. These were brought back to Mr. Cunningham by Scout.
2. Mayella's bruises were on the left side of her face. This suggests Tom's innocence because his left hand is crippled. It also suggests that maybe it was were father, Bob, who had hurt her, as he is a left handed man.
The children, Jem and Scout, have gone up to the jail and see Atticus sitting in the jail house door with his feet propped up. The mob that gathered at the jail house was an angry mob that smelled of staleness and whiskey. They had arrived in cars. The men are speaking in soft tones probably out of respect for Atticus.
The men try to get Atticus to get out of the doorway. Atticus tells Walter Cunningham to go home. Scout runs to her daddy pushing through the crowd. Atticus tries to send Jem and the children home. A burley man had grabbed Jem and Scout in reaction had kicked him.
The crowd continued to demand Tom Robinson. Scout sees Mr. Cunningham and starts talking to him about some of the things she had heard Atticus discuss. When Mr. Cunningham did not respond, Scout had asked him if he had not recognized her. She starts talking about Walter. Mr. Cunningham then had signaled the crowd to dissipate. The humility of the child trying to encourage small talk with her classmate's father had brought Mr. Cunningham back to reason.
The side of Mayella's bruises is significant because one of Tom's hands is useless.