The animals use the whistle-like sounds to communicate. Dolphins and porpoises send out the clicks into the water and the clicks bounce back off the objects around them. This is how they hunt for fish and navigate. Scientists still don't agree on exactly how it works. But here's what many think.
Scientists think the sounds are created just below the animals' blowhole, in their nasal passages.
The melon is filled with an oily substance which focuses or directs the sound forward, in a sort of beam. Scientists think the echoed sounds or vibrations are received by the animals' lower jaw, and then passed to the middle ear and brain for processing. The clicks sent out by dolphins and porpoises help them to hunt for food by showing them where it is. The sounds may temporarily stun nearby fish, making them easy prey. If dolphins' and porpoises' navigation systems are disturbed or hurt, it can kill them.