Explain the incident at the jail when the mob formed and Atticus was in danger.

The mob was a lynch mob, plain and simple, with the
purpose of removing Tom Robinson from the jail and carrying out vigilante justice the
old fashioned Southern way. . .by lynching Tom Robinson.  Atticus anticipated this, of
course, which is why he was sitting outside reading a newspaper; what no one did
anticipate, of course, was the arrival of Scout and Jem, nor did anyone expect the mob
to disperse after Scout's innocent inquiries into Mr. Cunningham's well-being and the
state of his "entailment".  Some have argued that this scene is not realistic, but many
believe that Scout's innocence in the face of such hatred and dangerous mob mentality
was completely realistic.