Ferals (Tales of the Half-Bloods)

A Feral is a Half-Blood (Think of Minotaur, Centaur, Merfolk and the like) that has lost his or her mind to the human side. This only occurs in humans that have changed from fully human into a Half-Blood. Once the mind is lost, animal instincts take over and causing said being to behave accordingly. 

Due to both the original Mind and the new Half-Blood mind inhabiting the same body, this causes a war within one's own body. From nightmares to visions of things one would rather not witness, the fight for the new body continues until one side of the Half-Blood wins, the old human mind or the new Half-Blood mind.

It is highly seen as charitable to end the life of a Feral, to ease the suffering and prevent more harm from happening.