"Well how do you know we ain't Negroes?"
"Uncle Jack Finch says we really don't know. He says as far as he can trace back the Finches we ain't, but for all he knows we mighta come straight out of Ethiopia durin' the Old Testament."
"Well if we came out durin' the Old Testament it's too long ago to matter."
"That's what I thought," said Jem, "but around here once you have a drop of Negro blood, that makes you all black." (16.78-81)
Jem and Scout here try to figure out how society divides people up into races, and what happens when those divisions break down. As kids who don't yet simply accept the existing system as the Way Things Are Just Because, they can see that the "one-drop rule" doesn't really work unless the origin of every drop of a person's blood (or every gene in their DNA, to update their science) can be accounted for, and why is one drop of black blood able to overwhelm several gallons of white blood, anyway? And how can blood have a racial identity? Oof. Someone pass the Tylenol.
Quote 2
So far, things were utterly dull: nobody had thundered, there were no arguments between opposing counsel, there was no drama; a grave disappointment to all present, it seemed. Atticus was proceeding amiably, as if he were involved in a title dispute. With his infinite capacity for calming turbulent seas, he could make a rape case as dry as a sermon. (17.56)
And all these people wanted was a fun day out, right? Atticus ruins everything with his fair, reasonable, and calm approach to deciding a man's fate. Spoilsport.
Quote 3
As Judge Taylor banged his gavel, Mr. Ewell was sitting smugly in the witness chair, surveying his handiwork. With one phrase he had turned happy picknickers into a sulky, tense, murmuring crowd, being slowly hypnotized by gavel taps lessening in intensity until the only sound in the courtroom was a dim pink-pink-pink: the judge might have been rapping the bench with a pencil. (17.95)
The courtroom spectators get what they came for with Mr. Ewell: sex, scandal, and hate-mongering. Notice how Judge Taylor calms them down by "hypnotizing" them. This isn't a crowd ready to listen to reason. (Let's put it this way—we wouldn't want to see them anywhere near a Wal-Mart on Black Friday morning.)