Thanks, but I already knew how the ballroom seen worked. My curiosity is about the ghosts who join you in the doom buggy at the end of the ride, especially how they swap heads on the people in the doom buggy. I am guessing that it may still use the reflection technology to merge your reflection with that of the ghosts, but with a wide video screen (sort of like the "strip" screens that go around a sports stadium) behind the doom buggy generating the images that move along with the doom buggy.
I love the behind the scenes tours at WDW that they have now, but the ULTIMATE tour for me would be an after hours tour where they showed you the "insides" of some of the rides. I would gladly stay up all night long for that kind of tour!