Slide 2 is where the pattern for the rest of the slides appears. Two hotspots of nearly equal size sit low on the slide: the left one returns to Slide 1, the right one moves on to Slide 3. Readers already turn pages that way, so nobody needed instructions.
The frame above is drawn at the original proportions. Each dashed box sits where the 2009 hotspot sat and links to the same screen it did then, so the tour can still be walked end to end.