First, the water level in a pond inexplicably plunged. Then, thousands of toads appeared on streets in a nearby province. Finally, just hours before China's worst earthquake in three decades, animals at a local zoo began acting strangely. As bodies are pulled from the wreckage of Monday's quake, Chinese online chat rooms and blogs are buzzing with a question: Why did n't these natural signs alert the government that a disaster was coming? "If the seismological bureau were professional enough they could have predicted the earthquake ten days earlier, when several thousand cubic metres of water disappeared within an hour in Hubei, but the bureau there dismissed it," one commentator wrote. In fact, seismologists say, it is practically impossible to predict when and where an earthquake will strike. Several countries, including China, have sought to use changes in nature, mostly animal behaviour, as an early warning sign. But so far, no reliable way has been found to use animals to predict earthquakes, said Roger Musson, a seismologist with the British Geological Survey. That has not stopped a torrent of online discussion. Even the mainstream media chimed in, with an article in Tuesday's China Daily newspaper questioning why the government did not predict the earthquake. The first sign came about three weeks ago, when a large volume of water suddenly disappeared from a pond in Enshi city in Hubei province, around 560 km east of the epicentre, according to media reports. Then, three days before the earthquake, thousands of toads roamed the streets of Mianzhu, a hard-hit city where at least 2,000 people have been reported killed. Mianzhu residents feared the toads were a sign of an approach ing natural disaster, but a local forestry bureau official said it was normal, the Huaxi Metropolitan newspaper reported on May 10, two days before the earthquake. The day of the earthquake, zebras banged their heads against their enclosure door at the zoo in Wuhan, more than 1,000 km east of the epicentre, according to the Wuhan Evening paper. Elephants swung their trunks wildly, almost hitting a staff member.