I don't know if anyone remembers but a while back there was an undead horse revealed, but I have no idea if it is even in Black Ops 2 Zombies as I have looked everywhere and tried everything but it is no where to be found..
Do you think it could be to do with the future DLC? Or possibly another secret easter egg on transit?
Theres quite a lot to tranzit people dont know about, such as you can make the wondergun. how to get to and make the pack a punch machine (inside the bank vault), where to get the bowie knife (helps with the flying golem things), getting inside a zombie hole and teleported to the other of the map (haven't done it myself, but im 99% sure thats how u get the "alternative means of transport" achievement on 360) etc.
have not heard anything of a horse though, but i didnt listen very closely before release time.