Why did the officer slap mama?Why doesn't anyone go to defend mam?

The soldier asks why the casket is closed, and Mama explains Great-Aunt Birte died of typhus and the doctors have warned them that the corpse could still be contagious. However, she offers to open it anyway if the officer wants to have a look. He slaps Mama and the soldiers leave. Retaliating would surely get them discovered and arrested.