What is Hannah's flashback in Chapter 2 ?

When she was younger she had been fascinated by the five-digit number tattooed on his arm. After Aaron's bris, she had taken a blue ballpoint pen and written five digits on her own arm, thinking it would please him. When she showed it to him he had become irate screamed, "Malach ha-mavis" at her, frightening her. She still has nightmares about the incident and has not been able to forgive him for it.