Actually human fingernails and hair are made up of the same substance, just in diffirent forms, that naturally is a straight material, which is Keratin. Much like how graphite and diamonds are both made up of carbon, but are yet diffirent.
The rhino ‘horn’ is not a real horn but thickly matted hair, consisting of ""((Keratin, the same chemical substance that our finger nails and hair are made of."")) If a rhinos horn is broken off, it will grow back again. A rhinos horn grows all through its lifetime and grows at a rate of 1 – 3 inches per year, the longest recorded rhino horn is 5 feet long.