According to the Flower Bomb blog ( a new to me blog), there's an art space near Cobble Hill in New York called the Invisible Dog, where the original invisible-dog toy was invented. And they held an Improv Everywhere stunt last month where they loaned out over 2000 "invisible dogs" down the streets of Brooklyn on a Sunday afternoon. The mission: to catch people arriving in the neighborhood from the subway or wherever, notice somebody walking an invisible dog, think that's weird and then on their way home see about 500 more.

theinvisibledog.org