The attached 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 learned this, or if it is an inbred ability.

 

The dolphin does a quick flip of its head and a silver ring appears in front of its pointed beak. The ring is a solid , donut shaped bubble about 2 feet across, yet it doesn’t rise to the surface of the water.  The dolphin then pulls a small silver donut from the larger one.  Looking at the twisting ring for one last time, a bite is taken from it, causing the small ring to collapse into thousands of tiny bubbles which head up to the water’s surface  After a few minutes, the dolphin creates another ring to play with.  There also seems to be a separate mechanism for producing the smaller rings, which a dolphin can accomplish with a quick flip of its head.

 

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 the dolphin’s dorsal fin when it is moving rapidly and turning.  When dolphins break the line, the ends are drawn together in 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 blow hole.  The energy of the water vortex is enough to keep the bubbles for a reasonably few seconds of play time.

 

Video shows dolphins playing with bubble rings. (2.2 mb)