Book 33, Question 78
What are hooves, claws, and nails made of?
Hooves, claws, and nails are all made of keratin, a tough protein.
Your fingernails and hair are made of keratin, too. In a horse, keratin forms a thick, hard hoof. In a cat, it shapes a sharp, curved claw. In a monkey, it forms a flat nail. The material is the same, but the shape changes to match the job. Keratin grows from the base and wears off at the tip.