This is a trimmed chestnut. They grow a material similar to a nail or horse hoof - ergots are similar, but in a different location. When they get big you just peel or clip it off. They can smell a bit strong when you trim them, but hooves smell worse when the farrier comes out!

It’s actually a really interesting question. It’s commonly believed that on horses the vestigial remnants of additional toes/hooves/foot structure are the chestnuts and ergots. The first known horse had 3 and 4 hooves per leg!

Yes! And they’re always walking on their middle fingers.