As usual, I'm glad to know you like where this is going, Bob. :)

I am curious, though... if there is one aspect of the original version you'd like me to keep, what would that be?

As for my choice in words... Well, I never really knew about that, but regardless I've always thought of body language as a form of communication anyhow. Perhaps this instead?
I blinked at the sudden transformation the class went through. At first they seemed so derisive in how they stared at me. 'Contemptuous' might be a better word for it, but by Raven's feathered nutsack I swear you can communicate unbridled derision with just a glance if you try hard enough. As for the students sudden change in behavior... Needless to say, I was caught by surprise.
How's that?  As a bonus, it adds a bit of color, too.