The anatomy of self-propelling objects is subject to universal laws. Those of cars and animals are similar in many ways. First of all, there's the stomach. Stomachs are like petrol tanks. It takes energy to move around, and that energy must accompany its user. All self-propelling objects carry provisions with them in a sealed-off space, a stomach or a tank. Self-propelling beach animals like Animaris Percipiere have a stomach too. This consists of recycled plastic bottles containing air that can be pumped up to a high pressure by the wind.

p. 153 - The Great Pretender. (2007)