Threshers are easy to identify by their extremely long tail fin. The top part of the tail fins is often longer than the body itself. The shark uses its long tail to hunt schools of fish. It swims in continually smaller circles around the school while thrashing its tail. And then it attacks. Threshers can produce quite a clap with their tail. Sometimes a bird is hit unconscious. As long as they don't feel threatened, threshers are not dangerous for humans.