One task for scientists today is to learn exactly which types of animal behavior predict quakes. It's not an easy job. First of all, not every animal reacts to the danger of an earthquake.

　　Just before a California quake in 1977, for example, an Arabian horse became very nervous and tried to break out of his enclosure. The Australian horse next to him, however, remained perfectly calm. It's also difficult at times to tell the difference between normal animal restlessness and “earthquake nerves”．A zoo keeper once called earthquake researchers, saying that his cougar had been acting strangely. It turned out that the cat had an upset stomach.

　　A second task for scientists is to find out exactly what kind of warnings the animals receive. They know that animals sense far more of the world than humans do. Many animals can see, hear, and smell things that people do not even notice. Some can sense tiny changes in air pressure, gravity, or the magnetism of the earth. This extra sense probably helps animals predict quakes.

　　A good example of this occurred with a group of dogs. They were shut in an area that was being shaken by a series of tiny earthquakes.(Several small quakes often come before or after a large one. ) Before each quake a low booming sound was heard. Each boom caused the dogs to bark wildly. Then the dogs began to bark during a silent period. A scientist who was recording quakes looked at his machine. It was acting as though there were a loud noise too. The scientist realized that the dogs had reacted to a booming noise. They also sensed the tiny quakes that followed it. The machine recorded both, though humans felt and heard nothing.

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