Sharks whip their tails to stun prey, a sign of \"intelligent\" hunting behavior previously observed only in marine mammals, British scientists say. Underwater footage of thresher sharks taken in the Philippines revealed that when they hunt they first stun their prey by unleashing a powerful shock wave with their tails, the researchers said. The sharks use their lengthy tail fins to stun and swat sardines from shoals. Such use of the tail fin during hunting -- previously observed only in mammals such as dolphins and killer whales -- might indicate sharks are more intelligent than previously thought, the researchers said. Writing in the journal PLoS ONE, the researchers describe how the sharks can swipe their tails through an arc of 180 degrees in just one-third of a second to hit fish and create a stunning shock wave. \"It\'s very violent, very quick and very dramatic,\" said study lead author Simon Oliver, founder of the Thresher Shark Research and Conservation Project. While it has long been suspected the thresher shark\'s tail, about as long as the rest of its body, was used to hunt, the video footage is the first formal documentation of the behavior, he said. \"I had been chasing these animals for five or six years.\" Oliver, based at the University of Liverpool, said.