Mayella Ewell was primarily beaten on the right side of her face according to her testimony in the trial in Harper Lee's novel "To Kill a Mockingbird."
Mayella had bruises on the right side of her face. So if someone would of attacked her and hit her in the face they would probably be dominant in their left hand. Toms left arm is significantly shorter than his right due to a farm injury.
Tom Robinson's left arm is useless. It hangs limply at his side. So much so, that he can't even keep it laid on a Bible in order to raise his right hand to take the oath. Mayella Newell was beaten on the right side of her face. Since the person who beat her up was facing her, that person MUST have used his left hand. (If he had been using his right hand he would have beaten the LEFT side of Mayella's face.) It is obvious to EVERYONE in the courtroom (except the Newells) that it was physically impossible for Tom Robinson to have beaten Mayella. If that part was a lie, then the entire rape/assault must have been a lie, too.
Mr. Tate and Mr. Gilmer testify that Mayella Ewell was beaten on the right side of her face, suggesting that the assailant was left-handed. This information is used to imply that Tom Robinson, who had a disabled left arm, was the one responsible for the attack.
In Heck Tate's evidence, the main points are that he found Mayella Ewell beaten up and claimed that Tom Robinson was the one responsible. During Atticus's cross-examination, he reveals that there were no medical reports to confirm the extent of Mayella's injuries and questions Tate's assumption that Tom was the culprit based on Mayella's testimony. Atticus also highlights inconsistencies in Tate's account of events.
By having Bob Ewell write his name on the envelope, Atticus proves that Bob Ewell is left-handed. This is significant because it suggests that Bob Ewell was the one who attacked Mayella Ewell, as the evidence showed that the attacker must have been left-handed.
Mayella's bruises on the right side of her face were important because they indicated that she was most likely struck by a left-handed person. This detail became significant during the trial to suggest Tom Robinson's innocence, as he had a non-functional left arm and could not have physically inflicted the injuries on her right side.
"He first explains that "She was pretty well beat up". Then says "Well, she was beaten around the head. There was already bruises comin' on her arms. She also had a black eye. Right eye." Rate This Answer
Tom Robinson had a deformed left hand.
The fact that Mr. Ewell was left-handed was significant because it indicated that he was likely the one who beat Mayella on the right side of her face. A left-handed person would naturally strike with their left hand, causing injuries on the right side of the victim. This inconsistency in the evidence pointed to Mr. Ewell's guilt in the assault.
Atticus asks Mr. Bob Ewell to write his name on a piece of paper while he is cross examining him. Mr. Ewell writes his name with his left hand, so he is left handed, which proves that Tom Robinson could not have raped and beaten Ms. Mayella Ewell, because Tom Robinson's left arm is completely crippled from an accident he had long ago. Ms. Mayella Ewell had been beaten on the right side of her body. Atticus shows that it was Bob Ewell who beat Mayella, but due to the racism in Maycomb, Tom Robinson was wrongly convicted as a black man.
Atticus wants to reveal that it is unlikely that Mayella's injuries were caused by Tom Robinson because they were on the right side of her face, suggesting that someone with a left hand was responsible. This challenges the prosecution's assertion that Tom is guilty.
The audience sees that Bob Ewell is left-handed when Mr. Gilmer asks him if he is ambidextrous. Bob Ewell confirms that he uses his left hand for most things, like signing his name. This detail becomes important later in the trial as it points to Bob Ewell being the likely assailant in the attack on Mayella Ewell.