Dolphins are one of the smartest animals on Earth. They can perform tricks and perform on command if they are taught by a human. Dolphins usually grey, blackish, or brown , and are about 1-4 metres long. Dolphins feed primarily on fish, and most of them are gregarious, appearing in groups of a few to several hundred. A number of species are attracted by moving ships, often accompanying them or leaping alongside and sometimes riding the wave created by the moving bow. The bottle-nosed dolphin, characterised by a "built-in smile" formed by the curvature of its mouth, has become a familiar performer in oceanaria. It has also become the subject of scientific studies because of its apparent intelligence and its ability to communicate with its kind through a range of sounds and ultrasonic pulses. Dolphins are the smartest animals alive,so Humans have studied them a lot over the years.