How to form smoke rings?
A smoke ring is a visible vortex ring formed by smoke in a clear atmosphere.
Smokers may blow smoke rings from the mouth, intentionally or accidentally. Smoke rings may also be formed by sudden bursts of fire (such as lighting and immediately putting out a cigarette lighter), by shaking a smoke source (such as an incense stick) up and down, by firing certain types of artillery, or by the use of special devices, such as vortex ring toys. The head of a mushroom cloud is a large smoke ring.
When blown in still air, a smoke ring usually travels roughly straight from the opening over a surprisingly large distance, maintaining its shape, until dispersed by turbulence or other interference
http://en.wikipedia.org/wiki/Smoke_ring
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