In chapter 2 of The Devil's Arithmetic, Hannah has just arrived at her grandparents' home for the Passover Seder. Her grandfather is watching the television and is very upset, gesturing emphatically and yelling in both English and Yiddish. The whole family is gathered around him as they try to calm him down.
It is what is being shown on the television that has Grandpa Will so distraught. Across the screen are images of the concentration camps of the Holocaust. As Grandpa Will shouts angrily at the TV, he brandishes the tattoo on his arm. The television program has dredged up terrible memories for him. It has reminded him of when he was a teenage boy in the concentration camps. During that traumatic time, Grandpa Will had been tasked with disposing of the bodies of his fellow Jews who had been murdered. For a time he had given up all hope of his own survival. Now, many years later, he clearly still experiences feelings of anger for what he and so many others went through.
Although the adults all seem to understand Grandpa Will's behavior, Hannah is confused and embarrassed. She asks her mother why he does not just put it all behind him. Over the course of this book, Hannah comes to understand for herself that the past cannot and should not be forgotten.