Sperm whales make the loudest communication sound of any animal on Earth, researchers find — but they aren't sure why. Sperm whales (Physeter macrocephalus) are the largest toothed predators, growing up to around 59 feet (18 meters) long. The distinctive clangs, first reported in the 1980s , are the loudest communication signal that sperm whales make, although they can produce even louder echolocation clicks to locate prey during hunts. To make the clangs, male whales use their "phonic lips" ‪—‬ structures in their noses that snap together. In future studies, the researchers hope to learn more about this mysterious form of communication by playing recordings of the clangs underwater and seeing how nearby sperm whales respond.