In a vast
cubicle office environment, when one stands up in one's own cube and looks along the tops of the many
cube walls stretching out to the horizon. The cube horizon can be interrupted by the heads of people walking around. And by many
heads at once if there is a loud, unexplained noise
in the area. This
can result in a phenomenom called prairie-dogging
people stand up and look around like prairie dogs coming
out of their holes.
I first came across "cube horizon" in James Hynes' novel "Kings of Infinite Space."