A bubble ring is a quantity of air formed into a ring shape, which is traveling through water. The ring spins as it travels through the water, much like a flexible bracelet might spin when it is rolled off a person's arm. Some scuba divers can create bubble rings by blowing air out of their mouth in a particular manner. Bubble rings and smoke rings are both forms of vortex rings , and are sometimes studies in the field of fluid dynamics. Dolphins and humpback whales have also been seen to deliberately create bubble rings.