[icedog]

Besides the arrow keys, you can move forwards or backwards by clicking on the left or right edges of a slide.

[sdenton4]

The left and right buttons also do the trick.

[zellyn]

You can also click on the vertical area between slides to go forward/back.

[integraton]

Also known as "easter egg navigation."

[enneff]

It's a tool for giving presentations, not necessarily for reading them.

But I've just sent a change to add some help text to these pages: https://go-review.googlesource.com/4910

edit: The change is now live. No more easter egg navigation. Yay!