It is difficult to study dolphin speak in the sea because dolphins swim very quickly. Also, it seems that one sound can mean many different things. For example, when they are fighting, dolphins clap their mouths to say go away!" But they make the same sound when they are playing. It's like humans. When you raise a hand, it might mean hello, good- bye, or stop. Scientists still don't understand everything dolphins say but one day, who knows, maybe you'll get a phone call from a dolphin.