All dolphins and porpoises have these abilities, but some are more willing than others to share them with man. The star performers at sea aquariums and in research work are usually bottle-nosed dolphins. "Flipper" of television and movie fame was a bottle-nosed dolphin. Such dolphins appear to thoroughly enjoy man's company. They do not learn tricks the ways dogs do. But dolphins cannot be taught to do tricks that they do not want to do. When a dolphin does learn a game or trick, the animal seems to understand the purpose of the game, and it may even add some ideas of its own. Scientists are discoring that man's kinship with dolphins and porpoises is very great. We both have language. We are both intelligent. We both try to help friends and neighbors in trouble. And we both get stomach ulcers from worry. Dolphins carry on conversations with each other. So do porpoises and, probably, other whales. They make a great variety of sounds, mainly clicks and whistles, which are produced by a complex groups of air sacs and valves in the head. (They do not have vocal chords like man's.) if one dolphin of a group is caught in a trap, it appears to warn the others, not just of general danger, but specifically what and where the danger is. The dolphins then seem to discuss how to release the trapped one and carry out their plan. Each animal continually sends out an echo-sounding signal that locates prey, obstacles, and any other objects in the water. When a dolphin is resting, one signal is emitted every 20 seconds. When actively hunting, a dolphin rends out about five signals every second. A very complex brain--perhaps as complex as man's--picks out the specific echo the animal is interested in from the thousand of sounds and echoes always bouncing through the sea. They have no outer ear, just a tiny pinhole a few inches behind the eyes.