Eliminate the Impossible

I can't believe I forgot to upload this! It was sitting around in my Fabriano sketchbook when I found it after drawing it a few weeks ago, mainly in a car and in a waiting room. That's where we all get most of our art done, am I right?  

Drawn with graphite pencil and touched up with Adobe Photoshop. 

UPDATE: This drawing is on the bulletin board for visitor comments and artwork at 221B Baker Street in London. It may since have been rotated off, but as far as I know, it's still there.