Louis nods at Christopher when he enters the class, simply putting the stumble down to a moment of clumsiness instead of surprise. However, when he turns back to the blackboard, he ends up frowning. They're supposed to be studying musical tones, but for some reason he's written "Deceptive Cadences" on the board instead. There's even notes about how they trick the ear and make you hear the unexpected. Frowning, he starts to erase that bit, waving his hand at the seated students in a general "hold on" gesture.