It's not in gear. Burning a lot of the fuel outside the engine is inefficient. This display is intended to show flames, not power. The flame effect is produced by deliberately misfiring the engine every second or third cycle, or by momentarily turning the spark off altogether, and then igniting the unburned fuel/air mixture at the end of the exhaust pipe. Loading the crankshaft would have decreased the amount of time the spark can be depowered without stalling the engine. The engine can revert to normal operation without misfire when you want the car to move.