Summoned by e-mails, random strangers have been gathering at specific times in predetermined places this summer to engage in miscellaneous collective action. If this sounds vague, that's because it is. Whether the phenomenon, referred to as a "flash mob," is a cure for the ennui of the wired generation or an incipient form of social protest may be open to debate. But what is clear is that flash mobbing is global, and it's spreading. One mob recently gathered in New York City's Central Park, mimicked bird calls and chanted "Nature, nature" for 20 seconds at 7:26 p.m. and then left. Another crowd stopped in the middle of a busy Berlin street to shout into their cell phones. Some participants claim flash mobs unite strangers and create communities, but not all resort to such high-minded justifications. "We're part of the biggest group of losers in London," said a 21-year-old office administrator, sitting in a pub on Tottenham Court Road last week, before he and a friend made their way to a sofa store to join the city's very first flash mob. Along with 200 other Londoners, they gathered in the shop for 10 minutes and then left, to the befuddlement of the manager. No one knows how many flash mobs have taken place so far. But their popularity may already have sown the seeds of their demise. Participants are worried that they'll soon be outnumbered by reporters.