Those old enough to remember the Grimtooth's Traps series will fondly recall this handy device.
Commonly hidden in easily accessible stairways of dungeons* to aid in the elimination of delvers. When occupied by a suitable mass of delvers, the stairway slats rotate to convert into a series of extremely sharp steel blades. Aided by the slope, the delvers make rapid and uncomfy progress to whatever gruesome fate awaits them.
* In RPGs and computer games. Of course.