Although the trial of Tom Robinson was over and Tom Robinson was dead, the Ewells are having trouble letting bygones be bygones. Specifically, Bob Ewell knew enough to know that Atticus and Judge Taylor had made him look foolish on the witness stand, and has been heard around town making ominous comments like "One down, two to go", foreshadowing his plans to harm Jem and Scout. He spits on Atticus in town one day, tells everyone that Atticus is the reason he lost his WPA job, and breaks into Judge Taylor's home late one night.
The day that Atticus and Calpurnia went to tell Helen Robinson of Tom's death, some of the Ewells yelled and heckled them as they passed back by the Ewell house. The Ewells also threw rocks at Helen as she walked by their house, and once Ewell followed Helen muttering obscenities as she walked to work, until Link Deas told him in no uncertain terms that Helen was to be left alone.
Taken individually, these events are confirmation of the character, or lack thereof, of Bob Ewell; taken together, they are ominous signs foreshadowing what is to come for Jem and Scout, what Scout will call "our longest journey together".