User blog comment:Jamesfury/Red Dead Mythbusters/@comment-1429911-20100619160756

The Zombie Horse is just a reskinned horse from one of John's missions, I think the one where we find all those people killed by the W-Gang. Anyway, that one does sound like an AI glitch, but an AI glitch more along the lines of the donkey woman. It looks like Lobo's AI got mixed up with a human skin, and somehow modified it. Overall, that sounds like a very, very interesting glitch.