why does the french girl advise elie to "bite your lips, little brother?

Another time, while Elie is working at the electrical warehouse, Idek the Kapo goes on one of his fits of rage and beats him. A young French girl that Elie works next to, aids him by wiping his bloodied lips. She slips a bit of bread into Elie's hand and tells him in perfect German, "'Bite your lip, little brother....Keep your anger and hatred for another day, for later on. The day will come, but not now....Wait. Grit your teeth and wait....'"