Find the book that's currently nearest to you. Why's it there?(If you want to do something a bit more interesting, you could do "Turn to page 126; find something on that page that's related to why the book is there. What is it, and why's it there?" Or, for that matter, pick the fifth sentence and ask whether it's interesting and why. But that seems extraneous at this point in the evolution.)
In my case, looks like it's Sagaut and Cambon's recent textbook on Homogeneous Turbulence Dynamics. At a surface level, it's there because rosefox sent it to me, in a box of other interesting and amusing books. She'd asked me if I would be interested in it, and I said, "Yes, very much." My doctoral dissertation work was on theories of computing the behavior fluid sprays, using mathematical stuff that's very similar to how turbulent flows are generally computed. So this is interesting to me on that front, as sort of a compendium of all of the current knowledge in that area; it's also nice to have as an artifact and reminder of that field of interest, since I've been moving away from it quite a bit with my current job, and I'm sad to be leaving it behind even as I'm happy to be doing the new things I'm doing.
I guess that explains why the book is in my house. It's on the desk behind the couch because that's where I put it after I unpacked it from the box and looked through it. And, which I should figure out which shelf it goes on and put it there, my books are still rather shuffled about and unsorted, and the top of the desk was there and empty -- because I'd just cleared it off and taken it to the wood shop for some smoothing, in preparation for the final sanding and application of stain and polyacrylic varnish that it needs in order to be actually done.