The first crack in his stoic mask appeared when she mentioned Oliver. Clearly her son's presence was a new fact for him. Perhaps he just assumed she was hiding there alone with Augustus. She hoped that he didn't continue to put the pieces together that Antonin was staying there too. He might be willing to keep her safe and even her son if she asked, but not betraying the known location of the wizard hated most by his uncle's faction might've been an unforgivable offense. To save his own family, and even himself, it was possible that he would have to reveal where the Dolohovs were hiding. She started to make mental plans for running again... with her family this time.