Black ring hovered above Nottingham industrial estate after propane unit exploded | Daily Mail Online
Explained: What is the mysterious Black ring hovering in the skies of Pakistan - Oneindia News
Strange Evidence: The Chicago Smoke Rings | This ring floating above Chicago caused a panic. Experts quickly shut down UFO talk, determining it's made by some kind of electricity. Worse? They're...
Giant Smoke Ring Maker Burning Man 2012 105 - Duncan.co