Today I saw "it"

     I was playing with the dog in the den. I was sitting on the floor, facing the library door, and the dog was in front of me, we were playing tug with one of his many toys. I distinctly saw someone wearing dark clothes with a white collar walk into the library. Thinking it was my wife, I  made a remark about the dog; but got no response. I got up and walked to the library door, no one was there. Noone could have left the library without my having seen them. I then went through the library and through the dinning room into the kitchen where my wife was working on a craft project. I ask her if she had gone into the library for anything and she replied ,"no". This is the first time that I've seen a "human" enity. My wife saw the child; we have both been witness to a small white with brown spotted dog on the rear staircase; but this is my first encounter. Strange, it happened so fast I really had no time to react to it. I do not remember the head, but plainly remember the dark clothing with a spot of white about were the collar would be.