I've just noticed a small section of the video is missing (at 2:39), my apologies for that, i've no idea how that happened, just checked the original and it's all there, must be a RU-vid upload glitch. In the mean time, if you're wondering what was missing it was only two steps: 1. I added a single edge loop top to bottom and pushed it along the X to create the width of the spine. 2. I selected the faces of the pages and extruded them along the normals (alt+E > extrude along normals) to inset them Also, Screencast Keys why do you keep failing on me!
