Suddenly, in the middle of New York City -- or Vienna, or Rome, or Tokyo -- a crowd starts to gather, randomly summoned via the Internet. Each person holds a piece of paper, glancing around, watching the others for a signal. Then silently, the crowd galvanizes, coalesces, swarms and -- with no forewarning -- breaks out in a demonstration as purely meaningless as abstract dance.

In Rome earlier this month, a throng flowed up a bookstore's main escalator, assembled without a word on the second floor, clapped for 15 seconds, then just as silently flowed away again down the escalator. In New York, where the fad originated this summer, a crowd gathered one day in the rug section of Macy's department store, stood around a certain rug, debated its merits for a while and then dispersed, much to the salespeople's confusion. In London, 200 people showed up at a West end sofa store to admire the merchandise and then disappear.

And two months ago, hundreds of people disguised as Agent Smith, a character in "The Matrix: Reloaded," converged in Shibuya and Osaka after the movie's premiere.