A 'feral' is a slur in the universe of Heyoke the Wolf as well as a medical term for a member of any species who has completely succumbed to the rot. Feral animals are said to have completely lost their humanity, becoming indistinguishable from the animals that humans are typically familiar with. Although becoming feral is typically associated with the lower bloodlines, any animal no matter the species or social caste can become feral in the same way one can succumb to depression or other mental illness. Some older high-blooded wolves for example are known to have been slowly losing their minds for the past fifty years. To become feral is the ultimate fate of every species in Heyoke's world.

The rabbits of Antioch have a serious problem with the proles becoming feral, leading to swaths of constantly-breeding sometimes violent feral districts whose inhabitants can't even communicate with their own government.