Mystery of the Silver Rings

The young dolphin gives a quick flip of her head, and an undulating silver ring appears--as if by magic--in front of her. The ring is a solid, toroidal bubble two feet across--and yet it does not rise to the surface! It stands erect in the water like the rim of a magic mirror, or the doorway to an unseen dimension. For long seconds the dolphin regards its creation, from varying aspects and angles, with its vision and sonar. Seemingly making a judgement, the dolphin then quickly pulls a small silver donut from the larger structure, which collapses into small bubbles. She then "pushes" the donut, which stays just inches ahead of her rostrum, perhaps 20 feet over a period of up to 10 seconds. Then, stopping again, she regards the twisting ring for a last time and bites it--causing it to collapse into a thousand tiny bubbles which head--as they should--for the water's surface. After a few moments of reflection, she creates another.
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thanks to plep