There was a famous jockey that never lost a race. When asked how he achieved this, he replied, I whisper in the horse's ear: Roses are red, violets are blue. Horses that lose are made into glue.

Animal (origin) glue is made from connective tissue, found in hoofs, bones, tendons, ligaments, and cartilage in vertebrate animals.

Rendering plants are the recycling links in the food chain. They take fat and bone trimmings from grocery stores, waste scraps from restaurants, and dead animals. They cook the meat and fat products together and grind it up. It's used for animal feed and non-edible products like soap, various lubricants, and of course glue--the heavy kind that's used to glue furniture together, for example.