A horseshoe is a piece of steel that has been nailed to the bottom of a horse's hoof to protect it from being worn down. Horseshoes can also be made from aluminium, rubber, plastic or other metals. A horses hoof is just like a person's toenail, and the horse cannot feel the nails going through it. A person who fits horseshoes to a horse's hoof is called a farrier. Horseshoes are said to give good luck if they are hung on a door with the open end pointing upwards.