A simple demonstration will tests students' understanding of electrostatics. This puzzler stumps even experienced physics educators and is sure to entertain a physics class. A plastic rod is charged using a piece of animal fur. The rod is touched to an aluminum pop can, creating a faint popping sound indicating that charge is transferred to the can. Next, the rod is held next to the can. Will the can be attracted to the rod, repelled by the rod, or neither of these? Before they see the outcome, students must make a prediction and work to convince other students that their prediction is correct. Only after all arguments are exhausted is the answer revealed. A video provided here describes the demonstration.