Dog barks at something on the stairs

    Today, while I was decorating our Christmas tree, my wife opened the door from the diningroom and came into the parlour to see how things were going. I had shut the dogs out of the parlour while working on the tree because their wild romping could have disasterous results. Needless to say they joyfully bounded into the room when my wife opened the door. The older dog stayed in the parlour with us as we discussed the tree. The younger one ran on into the hallway and bounded up the steps; stopping just before she reached the turn in the stairs,  and started barking frantically. Both of us quickly ran into the hall to see what the commotion was about. Standing stiff legged on the stairs the younster was staring dead ahead and having a fit. We saw nothing on the stairs. We called her, she ignored us and continued barking. Our older dog was standing beside my wife, whinning. I started up the stairs and the pup turned and beat a hasty retreat back down the stairs, went past me, past my wife and on into the parlour. I continued on upstairs to determine what up-set her so. I saw nothing unusual. My wife laughed and said, "Well I guess she saw the ghost". Interesting, that turn in the staircase is where I recorded the strange sounds that sounded like some stringed instrument being plucked and the photograph that appeared (to me at lest) to show the faint image of a womans head. I wondered if this new dog would react like the older one. Apparently she will.