Why does Aunt Alexandra continue to worry about the threat posed by Bob Ewell?
Having made the study of family and personality types one of her lifetime's achievements, Aunt Alexandra feels that the "poor white trash" Bob Ewell would sink to doing anything to get even with her brother Atticus for having exposed his failings to all in the courtroom during the trial of Tom Robinson.
When Bob Ewell spits in Atticus's face as he leaves the post office one day, Atticus merely takes out his handkerchief and wipes his face as he calmly replies to Ewell's insult that he is "too proud to fight" and is a "n****r-loving bastard" by saying, "No, too old." This behavior, Atticus later explains to Jem, is Ewell's way of finding some kind of comeback after his credibility at the trial was destroyed. While Atticus is talking with Jem, Aunt Alexandra enters the room and hears her brother tell Jem, "We don't have anything to fear from Bob Ewell; he got it all out of his system that morning." She interjects, "I wouldn't be so sure of that, Atticus....His kind'd do anything to pay off a grudge. You know how those people are" (Ch.23). When Atticus asks what Ewell would do to him, his sister replies, "Something furtive....You may count on that" (Ch.23). Feeling that Ewell is not satisfied with the renewal of hostility with Atticus, Aunt Alexandra suspects him.
As it turns out, Aunt Alexandra's suspicion that Ewell will do something furtive is correct. For he sneaks up on Atticus's children one night with a knife, planning to commit murderous acts. Fortunately, Boo Radley intervenes on behalf of Jem and Scout.
It is rumored that Bob Ewell hinted at killing Atticus. Word around town said that after Tom Robinson was killed, Bob Ewell said "one down and about two more to go" (To Kill a Mockingbird, Chapter 25).
Helen, Tom's widow, has to walk by the Ewell house on her way to work. As she walks by, members of the Ewell family harass her. Helen starts walking another way just to avoid them. Bob Ewell also starts following her on the road, making crude comments to her. Meanwhile, someone breaks into Judge Taylor's house. Many people suspect that Bob Ewell did it.
When Aunt Alexandra hears about this, she recalls Bob Ewell's supposed threat. She does not like Bob Ewell's treatment of Helen, and she finds it strange that he would break into the judge's house. In addition to these things being wrong, it makes her worry that Bob Ewell is dangerous. She expresses her concerns to her brother about the matter:
"That man seems to have a permanent running grudge against everybody connected with that case. I know how that kind are about paying off grudges, but I don't understand why he should harbor one—he had his way in court, didn't he?" (Chapter 27).
Aunt Alexandra is puzzled as to why Bob Ewell is still angry. After all, Tom was found guilty and sent to prison. Still, she worries that he will harm Atticus. After all, he is bold enough to break into the judge's house while it looks like he is home.