What's the deal with the ghost horse?

[wh33t]

I don't know how they would all share a vision of a horse, unless it was through the power of suggestion. I'm pretty stuck on what to think. On one hand, how could they share the same hallucination, on the other hand, why would Datu lie about a horse?

Totally, and how would a horse even get in there? Is it someone in a costume perhaps?