My daughter and I have spent quite a bit of time with the dolphins off our coast (Florida), and we have never seen any play like they do in this video.



Dolphins are so adept with water, and their sonar so sharp that they create these rings by exhaling air into the vortices created by the movement of their fins through water. Apparently this behavior isn't all that uncommon, but alas I've never seen it in the wild or at a seaquarium.

Interesting facts about the dolphin brain

Dolphins have two sub-brains with independent blood supplies.
Only one of the dolphin's sub-brains sleeps at a time.
Each eye is connected to a single sub-brain
The dolphin brain has 10 percent of the human brain's visual imaging ability
The dolphin brain has 10 times the human brain's acoustical imaging ability

An interesting related post concerning a blind teenager who has developed his acoustic imaging to amazing acuity can be viewed by clicking here.