Atticus suggested that Mayella Ewell was likely injured by someone left-handed based on the bruises on her face. He believed it was her father, Bob Ewell, who was left-handed and had a history of being abusive towards his daughter.
Actually, Atticus doesnt mock Mayella. Mayella thinks Atticus is mocking her because he is caller her Ma'am and Miss Mayella, which she isnt used to.
Bob Ewell, who is Mayella's father, beat her up
Atticus suggested that Bob Ewell, Mayella's father, was responsible for hurting her. He argued that Bob Ewell abused and manipulated his daughter as a way to cover up his own actions.
The judge asks Mayella what she's scared of, and she points to Atticus
Mayella cries because she thinks Atticus will find out that her father really did it.
Bob Ewell or Mayella
"Tempting a Negro"
Mayella's reaction to Atticus' behavior in court is ironic because Atticus is the only person actually trying to defend her and seek justice for her, yet she is hostile towards him. Despite his efforts to help her, Mayella feels threatened by Atticus' questioning and sees him as an enemy due to her prejudiced views.
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Atticus aims to show that Mayella is not a reliable witness by poking holes in her story and highlighting inconsistencies. He tries to establish that Mayella's accusations against Tom Robinson are a result of her own personal issues and not based on factual events. Atticus demonstrates that her testimony lacks credibility, bringing into question the integrity of the case against Tom.
When Mayella is on the stand the question Atticus asks that makes her furious is "How?" She has just described how Tom Robinson choked and beat her, and Atticus asks Tom to stand up. This draws the jury's attention to the fact that Tom's left arm is useless, making it highly unlikely he was Mayella's attacker. When Tom stands, Atticus asks Mayella if Tom is the man who attacked. When she responds that he is, Atticus asks, "How?"
Mayella Ewell was surprised and taken aback by Atticus's politeness during the trial. She had likely never encountered someone treating her with respect and courtesy before, which made her uncomfortable and defensive.