|Rules and Regulations|
In Hindu mythology, the Horse represents the Cosmos, being linked to Varuna, although the Cosmic Horse is in fact White. Given the Hindu-inspired uses of symbology elsewhere in the show, however, this interpretation of the Black Horse may be significant...perhaps suggestive of a Cosmos gone wrong.
More generally, Horses are often held as symbols of power, fertility, grace, beauty and, very commonly, war. A pairing of White and Black Horses represents Life and Death, respectively, as well as the warring internal aspects of the soul...White for patience and sensibility, and Black for impulsive disobedience. Black Horses also tend to be portrayed for the most part as negative influences, foreshadows of death or destruction. They often appear in folklore as the mounts of charlatans, traitors, or even the Devil.
These aspects seem to suggest that the Black Horse may well symbolize Kate herself in many ways.