They are yelling “back off!” dolphins sometimes snap their jaws when staking out territory, warning other dolphins to keep away. Dolphins can produce extremely loud sounds by rapidly clamping their jaws together. This behavior bangs their teeth together, producing an acoustic signal that transmits large distances. Jaw claps are generally understood to be an aggressive signal, used as a threat. But jaw clapping also occurs during play – the difference between real aggression and play aggression is often very subtle, just like in the case of humans.
Picture Credit : Google