In to kill a mockingbird what question does atticus ask the sheriff three times?

When Sheriff Tate is on the stand Atticus asks him three times which side of her face Mayella's injuries were on. Sheriff Tate is confused at first and says her injuries are on the left, when he meant his left, and her right. This is significant because it implies a left handed attacker, and the man Mayella accused has a useless left arm.