Of all the marine mammals, dolphins seem like the only ones who really know how to cut loose and laugh. During playful situations, dolphins emit a certain sound that they don’t normally make in any other context. This sound, best described as several pulses accompanied by a whistle, only occurs when dolphins play fight with one another. Furthermore, dolphins don’t make this sound when they fight aggressively, indicating that the sound has nothing to do with fighting. Based on this evidence, scientists determined that sound is a vocalization of pleasure. At the very least, the sound is a sign that the dolphin’s actions are non-threatening. In a sense, dolphins laugh to let each other know that they’re okay. By laughing, they communicate their intentions and prevent a possible confrontation with another dolphin.

Source: A-Z Animals