That’s how a jellyfish swims. It sucks water by expanding its bell shaped body. As the body expands, a low pressure zone is created just under it. Water rushes in to fill that low pressure zone and the force propels the jellyfish in the ocean. It is the most energy efficient way of swimming. That method is much better than our submarines or ships. Even a flying machine can be built by using that method that will be far more efficient than a helicopter.