Flesh-Eating Horse

Flesh-Eating Horses are horses that feed on the flesh of other animals.

The Battle of the Labyrinth
While Percy was at the Triple G Ranch, he agreed to clean their stables (which were filled with the horses poop. Hercules had cleaned them using a river once before long ago, which the naiad was not happy about after it happened). Geryon mentions that they are great for cleaning up, but they are a real mess after. They tried to eat him, taunting Percy from behind the fence, so Percy sprayed them with salt water from petrified seashells while cleaning their stable until meat scraps had been washed out of their teeth and their dirty coats shined. They are the only horses that do not think of Percy as their "lord" but as seafood. After Percy threatened them not to eat any more people, just horse food or he would be back with more seashells, they agreed and promised they would be good flesh-eating horses from then on.

Trivia

 * The Flesh-Eating Horses are probably based on the Man-Eating Mares of King Diomedes.