Demonstrate the principle that a circuit must be complete for current to flow. Try to maneuver the wand along the wire without touching! If you touch, the circuit is completed and the light turns on.
An early version used a block of wood, with holes creted by pounding a nail, to spport the components. More recently we've gone to the cardboard version. The components are: some stiff uninsulated wire such as 14 gauge aluminum solid wire, an LED, and a 3V button battery.