I learned when I hear noises, to take my cell phone in to the area with me with my camera at the ready. I am glad I did.
On the right hand all of the books was all stacked normally. straight up. I went in took a fast picture, and noticed a shadow moving so I took a picture of that. Apparently Jacob was playing around with the books again.
The shadow was running from the bookshelf, toward a closet where I had caught him in a picture.
He is a great friendly spirit, and never causes harm. But he loves messing around with the books.