My co-worker Damien arrived at work yesterday carrying what looked like a small black wastebasket, and shot me with it. It was an Airzooka, an odd-looking device which shoots air. It works on the same principle as smoke rings, but more forcefully. The effect is literally astonishing, especially when the recipient gets hit in the face with an invisible bolus of fast-moving air. We were shooting things all day around the office. Good fun, I recommend it.

BTW: The "Learn More" link off the Airzooka page has some interesting articles about larger vortex generators (as these things are called), and about how smoke rings work in the first place.