You’d expect jellyfish to create areas of high pressure behind them, as they propel themselves along. They certainly do, but Dabiri saw that their undulating bells also create huge areas of low pressure in front of them. And these low-pressure areas accounted for a greater proportion of their forward thrust. The jellyfish weren’t primarily pushing themselves through the water, but pulling themselves forwards. They swam by sucking.
Fascinating read about how jellyfish actually swim and how a mechanical engineer's research has some potential far reaching implications in engineering motion in fluid, be it water, air or blood.