The incident at the jail when the lynch mob comes for Tom affects Jem and Scout differently. Jem had understood the danger to his father at the time, whereas the real nature of what had happened--and what could have happened--dawns upon Scout after the fact. When Jem defied his father's orders and refused to leave his side at the jail, he moved closer into an adult relationship with Atticus. Scout thought that after the mob dispersed, Atticus would have scolded Jem strongly, but instead, she noticed a different exchange between them:
As they passed under a streetlight, Atticus reached out and massaged Jem's hair, his one gesture of affection.
Jem and Atticus understood each other and what had just happened in their relationship. Later at home and the next morning, Jem continued to deal with events from an adult perspective and spoke about them, man to man, with his father at the breakfast table.
Scout, however, did not experience the incident from Jem's more adult perspective. The full weight of events hit her after returning home:
I was very tired, and was drifting into sleep when 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 full meaning of the night's events hit me and I began crying. Jem was awfully nice about it . . . .
By relating the lynch mob to the rabid dog Atticus had also faced, Scout recognized the terrible danger her father had faced, and the thought of it frightened her and moved her to tears. She was still her father's little girl.