I think he was so in shock and didn’t realize what was happening until it was over.
Even like that it shows in your face, not fully like opening wide the mouth and eyes. I think they could enhance it even more with his gaze, because when we see the teach's face we immediately see his eyes. But since he opened his eyes he stayed with almost the same face from beginning to end
Noooo! I’ve been noticing that every time he’s around blood he gets in this odd zone. Remember when he tried killing guwon in the first chapters? Yall gotta read outside the lines!
Come on now, I think they considered that too but a lack of emotion on a characters face is not always a good choice. in this case the emotions weren't conveyed properly to the audience and that's totally okay, not every face or panel can be perfect art wise. This is just some constructive critique on the comic and facial expressions are a big part of comic writing. The artist often draws teacher twink very stiff which I think is something they could work on from an art perspective. Not everything is an artistic joice.
I must say that it kind of annoys me that the author draw the teach with very null facial expressions. I hoped he would be a little more surprised or shocked of how he discovered a new layer that he didn't see of Guwon. He kind of knew about because he heard of it, but he didn't saw it until now