Oskar's knees go weak. "This is an act of evil. [The septas in there did no harm to anyone/Those are our brothers in the Lord of Light]." His hands shake as he prays for guidance.
Chastise Oskar for not believing the vision of [R'hllor/the gods] until he saw with his own eyes.
Tell Oskar it's not too late to save them. Tarryl can still be stopped.