The two moods in the trial are suspense and humor.
In extremely tense trial, there is a need for comic relief. Although we learn a great deal about the Ewells and Tom Robinson through serious testimony, there are also moments of humor.
First of all, most of the trial’s mood is suspenseful. People have been waiting for the trial for a long time, and there is a great deal of anticipation.
The moon is suspenseful and tense when there is testimony about the alleged crime, such as when Atticus is asking Mayella about what happened to her.
"You seem sure enough that he choked you. All this time you were fighting back, remember? You 'kicked and hollered as loud as you could.' Do you remember him beating you about the face?" (ch 18)
This is a serious mood, but we also want to know what is going to happen next. We are on the edge of our seats as Heck Tate and Mayella testify, and during most of Tom’s own testimony. The stakes are high, and we know it.
Yet there are also moments of humor to break of the tense parts.
"Are you the father of Mayella Ewell?" was the next question.
"Well, if I ain't I can't do nothing about it now, her ma's dead," was the answer. (ch 18)
This response is met by laughter from the courtroom, because this is a joke. Judge Taylor does not approve, of course, and scolds Ewell about keeping his language proper. Although it is somewhat low humor, it does break up the tension.
The trial chapters continue for some time, and it would be difficult to keep the suspenseful mood for so long. Therefore Lee alternates between informative, suspenseful, and humorous to keep the reader interested.