In To Kill a Mockingbird, during the court testimony about Mayella's injuries, what key facts seem inportant to Atticus.

In Harper Lee's To Kill a
Mockingbird, Atticus is very careful regarding the testimony about Mayella
Ewell's "injuries." He is very concise when questioning Heck Tate, the sheriff, and even
thorough in his cross-examination of Mayella Ewell and Bob
Ewell.

The significance of this is to establish the
veracity or truthfulness of what the Ewells are accusing Tom Robinson of. This speaks to
two different concerns on Atticus' part. First, Atticus already knows that Tom has one
arm that is useless to him caused by an accident with a cotton gin when he was younger.
In connection with Tom's inability to harm Mayella based on the side of the face that
was damaged, is the question of Bob Ewell—not only is he his daughter's real attacker,
but whether he has an abusive nature in general as a
father?

First Jem notices the strategy Atticus is using by
asking questions about Mayella's life.

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Atticus was quietly building up before the jury a
picture of the Ewells' home
life.

Later, Atticus asks
Mayella what kind of father Bob Ewell is.

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"I mean, is he good to you, is he easy to get
along with?

"He does tollable, 'cept
when—"...

"Except when he's drinking?" asked Atticus so
gently that Mayella
nodded.

When Atticus
questions Tom Robinson, we learn that Mayella made advances toward
him, not the other way around. She kissed him because she wanted to
know what it was like: besides the "kissing" from her
father.

"She
 said she never kissed a grown man before an' she might as well kills a n***er. She says
what her papa do to her don't
count."

(Here is an
inference, based on Tom's testimony, that Mayella may also have been sexually abused by
her father.)  Tom then explains that when Mayella's father saw what she was doing
through the window, he went berserk.

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"I didn't wanna harm her, Mr. Finch, an' I say
lemme pass, but just when I say it Mr. Ewell yonder hollered through th'
window."

"What did he
say?"

Tom Robinson swallowed again, and his eyes widened.
"Somethin' not fittin' to say—not fittin' for these folks'n chillun to
hear—"

"What did he say, Tom? You must
tell the jury what he said.

Tom Robinson shut his eyes
tight. "He says you goddamn whore, I'll kill
ya."

Jem reports that Tom
Robinson's manners were nearly as good as Atticus'. As Atticus reports later, Tom tries
to get away without pushing Mayella, for…

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...if he dared to strike a white woman under any
circumstances [he could not have expected] to live
long.

However, by running
away, it also made Tom look guilty—Tom faces a serious predicament. There is really no
way he can come out of this situation unscathed.

All of
this information points to Atticus' intention of establishing that Tom had no use of his
left hand, that Bob Ewell was left-handed (and probably hit
Mayella), that Ewell was violent when he had been drinking, and that he threatened to
kill Mayella for kissing a black man. Atticus is trying to develop a case that clearly
demonstrates Tom's inability to carry out the deeds he is accused of, and therefore,
his innocence, and Bob Ewell's guilt in the
beating of Mayella, and lying in court.