What makes Odile realize that the war is on the way?

Odile is speaking to Miss Reeder when the Countess tells her they need to speak. Odile overhears their conversation. They are talking about books being evacuated from the university library in Strasbourg and how they need to plan ahead too in case they need to save their books. They also discuss getting gas masks. Odile realizes that war is on the way and she has to face that fact