An explanation of how dolphins make these silver rings is that they are
'air-core vortex rings'. Invisible, spinning vortices in the water are generated from the tip of a
dolphin's dorsal fin when it is moving rapidly and turning. When dolphins break the line, the ends are drawn together into a closed ring. The higher velocity fluid around the core of the vortex is at a lower pressure
than the fluid circulating farther away. Air is injected into the rings via bubbles released from the dolphin's blowhole. The energy of the water vortex is enough to keep the bubbles from rising for a reasonably few seconds of play time.