Air-breathing dolphins always produce bubbles when they expel air underwater. Besides bubble rings, dolphins also produce a wide variety of other bubble types. They occasionally emit bubble streams concurrent with vocal activity. When surprised, curious, or excited, dolphins often emit a rapid exhalation termed a bubble burst. Breathing in dolphins, unlike in other mammals, is solely under voluntary control, a crucial feature in their adaptation to a fully aquatic existence. Whereas the physics of ring formation is straightforward, the actual production of stable rings may require some practice, expertise, and forethought by the dolphins.