London -- A massive antiwar march against visiting US President George W. Bush turned grisly Thursday after demonstrators lost control of a giant papier-mache effigy of the president's head, setting off a gruesome chain reaction that left Trafalgar Square strewn about with hundreds of dazed peace activists, journalists, and thousands of abandoned, half-burnt swastika-and-stripes flags. Although no fatalities were reported, British public health officials estimated upwards of 1500 protesters were awaiting treatment at local hospitals for minor injuries and mange. The head was not injured.