Prof (pausing in the middle of lecture to examine his forearm): Damn, I'm bleeding all over the place. I wonder what happened... (he fumbles with his shirt sleeve, rolling it up to examine the cut.)
3L in last row: Soda water!
3L: Soda water will get the stain out.
Prof (looks to the door and then back at 3L): No, no. Soda water will have to wait. I can't leave my post!