When Atticus ask mayella questions about that night, he uses rapid-fire questioning. what detail trips Mayella up?

Atticus asks Mayella if she recalls Tom beating her. Mayella stumbles on this question,

“It’s an easy question, Miss Mayella, so I’ll try again. Do you remember him beating you about the face?” Atticus’s voice had lost its comfortableness; he was speaking in his arid, detached professional voice. “Do you remember him beating you about the face?”

“No, I don’t recollect if he hit me. I mean yes I do, he hit me.”