A fish called the Pacific lingcod has one of nature's toothiest mouths, with about 555 teeth lining its two sets of jaws. Now, a new study suggests that these fish lose teeth as fast as they grow them — at an astonishing rate of 20 per day. To understand how the Pacific lingcod's mouth looks and functions, first throw out almost everything you know about your own mouth. Instead of incisors, molars and canines, these fish have hundreds of sharp, near-microscopic teeth on their jaws. Their hard palate is also covered in hundreds of tiny dental stalactites. And behind one set of jaws lies another set of accessory jaws, called pharyngeal jaws, that the fish use to chew food much in the same way humans use molars. Because the Pacific lingcod's teeth are so small, figuring out how quickly these fish lose their teeth was not as simple as sweeping them from the aquarium floor. Instead, the researchers placed the lingcod in a tank filled with a dilute red dye, which stained the fish's teeth red. Later, the researchers moved the fish to a tank filled with a fluorescent green dye, which stained the teeth again. In total, they counted over 10,000 teeth across all 20 captive fish. They also found that the fish lose an average of roughly 20 teeth per day.