This video is of dolphins playing with silver colored rings which they have the ability to make under water to play with. It isn’t known how they learn this, or if it’s an inbred ability. The ring is a solid, donut shaped bubble about 2-ft across,yet it doesn’t rise to the surface of the water. 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 rapidlyand 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.