This doesn't really surprise him; he knows left-handedness is said to be bad luck, or a bodily failure like blindness or limblessness. He nods (like Lan Wangji, he hates these cruelties that have been visited upon Magnus, that Magnus talks about so easily, as if they were nothing -- but he expects the world to be a cruel place, so he tends to just take them in). "What does that mean, second-grade? A lesser teacher?"