Situation: I am looking at a bookshelf with two other bookshelves on my left and right and there is a chair behind me.
Alternative situations: I pick up a book from the bookshelf in front of me to put it in the backpack behind me. I am grabbing a book from the bookshelf in front of me to read while I sit on the chair behind me.
Question: What object is sitting on top of the first object you run into behind me?