Boo!

So, I was just vacuuming in the hallway of my building. All of a sudden, I heard a ca-thunk-ca-thunk sound. I turned around, and there was a 2x4, about 4 feet long, lying on the floor. Where the heck did that come from? I really don't think someone could have thrown it there.
The board was lying beneath this hideously ugly, ginormous mirror that hangs on the wall. My only guess is that it was hanging behind the mirror to maybe keep the mirror from scratching the wall.
I brought the board to the maintenance man, who shrugged and sighed, and said nothing surprises him anymore. I asked about my mirror theory, and he said he supposes that could be it, but doesn't really know why the board would be behind the mirror, since there are hooks that keep it away from the wall. Then he added that the building was built on an Indian burial ground, so it was probably a ghost.
So who knows...