The octopod-inspired propulsion system consists of four bulbs made from a flexible plastic polymer (sometimes called elastomer). Water is sucked into each bulb with an actuator. Whereas a squid or octopus has a muscular closure to seal water in the mantle, the synthetic reproduction uses a recirculation valve to keep water from flowing back out of the bulb. A hydraulic piston contracts the bulb via an integrated cable and the water is expelled with great force.