Scout makes a connection between the events that had happened the night before at the jail, and the time when Atticus shot a rabid dog which had threatened the neighborhood. As she is drifting into sleep, "the memory of Atticus calmly folding his newspaper and pushing back his hat became Atticus standing in the middle of an empty waiting street, pushing up his glasses". The connection brings to Scout "the full meaning of the night's events", and she begins crying (Ch.17).
Atticus had been sitting at the jail to protect Tom Robinson from those who might take the law into their own hands. When the children sneak out to make sure he is all right, they see that mob has indeed arrived to confront him. Since Atticus has carefully downplayed the danger of the situation to the children, Scout, with her childishly limited understanding, at first thinks that the mob is made up of friends and neighbors she knows, and is startled to discover "that these men (are) strangers". She recognizes only one member of the group, Mr. Cunningham, and although she is able to unwittingly defuse the situation by talking to him and reminding him about the ties they have to each other and the community, the danger that the Finches faced was real, and deadly beyond her understanding (Ch.16). She has known fear and danger like that only once before, and understands the gravity of what has happened only when she remembers Atticus standing alone on "a deserted, waiting street" to face a mad dog with only a small caliber rifle (Ch.10).