Last week I ran across a video of dolphins creating “bubble rings.” It’s both beautiful and fascinating on many levels, not the least of which is the behavior and intelligence of these animals. It appears they create a vortex ring and inject air into it. They then manipulate the ring, pushing it around and even biting off smaller rings. You have to see it to believe it.
Here’s a scholarly work on cognition and this behavior, and some analysis of the mechanics (and a lot of cool images) from deepocean.net. I’ve not reviewed this (and am not qualified to) but it looks interesting.
And I’ve been meaning to post this huge gallery and collection of links and images from the Fluid Mechanics Group at the National University of Singapore. Plenty on vortex rings there.