During the trial in To Kill a Mockingbird, what do the witnesses reveal about themselves? Sheriff Tate, Tom Robinson, Mr. Ewell and Mayella Ewell.

There is always much that is revealed about a person who
finds him or herself on the witness stand and under the obligation of telling the
truth.

Sheriff
Tate

First of all, Sheriff Tate is dressed
professionally in a business suit for the trial of Tom Robinson.  He answers the
prosecutor's questions succinctly, offering no more information than is necessary.  When
Atticus cross-examines, Sheriff Tate displays his admiration for the acuity of Atticus's
mind; for instance, when Atticus asks for clarification of the time of the incident at
the Ewell house as well as when he wants to know exactly which eye of Mayella has been
blackened, Tate smiles as he recognizes the precision of
Atticus.

Bob
Ewell

A hostile witness to begin with, Bob
Ewell reveals his ignorance as he attempts to villify Tom Robinson and implicate him as
the perpetrator of a crime.  His seething hatred is revealed in the pejorative terms
that he uses regarding Robinson, as well as his disrespect for his own daughter as he
speaks of her as "screamin' like a stuck hog inside the house---"  Ewell's attempts to
embellish his testimony, in contrast to the minimalist speech of Sherriff Tate, suggest
his ulterior motives.  His ignorance is evident when he fails to realize why Atticus has
him write his name and points to his being left-handed.

In
addition, other than having bathed and washed his hair, Ewell displays little respect in
the courtroom ashe swears and is crude in his language. He exhibits "a haughty
suspicion" of Atticus, suggesting that he has something to
hide. 

Mayella
Ewell

The repressive and abusive conditions
under which Mayella lives are clearly evident in this witness's appearance and
testimony.  When first questioned, she looks at the judge and bursts into tears,
indicating the stress that she feels.  However, she is not ignorant as her father is
because she protests against Atticus,

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"Don' wnt him doin' me like he done Papa, tryin'
to mke him out
left-handed...."

Unlike
Sheriff Tate, she embellishes her testimony as does her father. However, Scout points
out that Mayella has

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something stealthy about  hers [testimony] like a
steady-eyed cat with a twitchy
tail.

Throughout her
testimony, Mayella looks to her father and is "jumpy."  At one point, Mayella
contradicts herself when Atticus asks if her father has ever hit
her,

"No, I
don't recollect if he hit me.  I mean yes I do, he hit
me."

This slip of the truth
may be an unconscious effort on Mayella's part to seem honest, or, perhaps, a
subconscious play for sympathy.  At any rate, Mayella Ewell reveals herself as a rather
pitiable victim of her environment.

Tom
Robinson

Appropriately aligned to the symbol
of the mockingbird, Tom Robinson reveals himself as entirely guileless and decent.  He
never implies that Mayella has lied; he simply states that she may be mistaken in her
recollection. Without realizing the implications of anything that he says, Tom speaks
from his heart, the most truthful place in any human being.  Unknowingly, he utters
words that condemn him regardless of the accuracy and extent of the evidence to the
contrary.  For, when he says that he has felt sorry for Mayella, he a black man and she
a white woman, he has violated the social taboo that supersedes all litigation at the
time.