Inside the cart is a treadmill tied to a gearbox. Powering the treadmill is a horse. Temperature and heart rate sensors attached to the horse allow its condition to be monitored so that it doesn't get overworked. When the horse walks it moves the conveyor belt which through a gearbox drives an electric motor that drives the front wheels. Although the inventor doesn't mention it, there is even the possibility for co-generation if the horse's exhaust is collected and reprocessed or used to collect methane. No word on whether Mirhejazi plans to bring the Naturmobil to next year's Detroit Auto Show to compare it the third gen Prius. Thanks to Tom for the tip!