Collector quality pocket magic!
Three small brass cylinders are displayed. You place a small rod in one of the containers, seal it, then shake it to hear the rattling sound. You then visibly switch the three containers around, a la the classic Three Shell Game, and ask the spectator to find the container with the rod. No matter how quickly or slowly the containers are mixed, the spectator is never successful in finding the container that rattles, even if the container is marked!
This can be built into an excellent comedy routine! Utterly baffling!