Photo by Towfiqu barbhuiya. The word crepitus comes from the Latin for “creak” and shares its root with the word “decrepit”. Its modern medical usage is an umbrella term for the various sounds made by a moving joint, which can…

Photo by Tristan Perrier. About 56 million years ago, primates began a complicated evolutionary process moving away from having claws at the end of their digits to having what they have today: nails. Made from a protein called keratin, claws…