What has teeth but can never eat. below the wrist

in night, why are wiesel and his father evacuated from the auschwitz concentration camp? a massive escape makes the nazis question the security of auschwitz. they are assigned to work as laborers in a factory at another camp, buna. hitler has ordered that all remaining jews be relocated within german borders. the german army needs the camp guards to go to the battle front for a last-chance defense.