I put myself into the riddle, wondering how I would behave if I lived in the hypothetical situation put before me. My interviewers smiled, or perhaps smirked, as I considered possible solutions. There's a village full of polite people that has no reflective surfaces.
Every villager sees every other villager every day.
Some higher power identifies that there is at least one sinner among the people. Any person who has sinned is marked by the higher power, and must leave the village. No resident will give a sinner any indication that he is marked, but all of the sinners leave on the third day. If the waiter had stared at me, I'm sure that he would have seen my brow furrow until my eyes almost completely disappeared. Over the course of five hours, I balanced marbles, burned rope and designed an object model for Priceline.