A series of mini-explosions in London's transportation system, exactly two weeks after a series of major bombings, have produced some of the same panic but not, it seems, anything like the large casualties seen there. So what's going on? A hoax? A series of duds? A warning: "We could do a big one again anytime if we wanted to"? Or—far more disturbing—an attempt to disperse some kind of chemical or biological agent with a delayed effect? Whatever it was, the BBC has set up a kind of reporters' blog with regular updates.