A sim-cage is a terran mechanical device used to train reapers in Icehouse. It was a coffin-shaped machine with a series of bulbs, wires and straps. It fed lights and sounds directly into a reaper candidate's brain, chosen to inspire emotions. Ecstatic joy would be followed by mind-numbing despair.
All inmates responded to the treatment the same; crawling on the floor, weeping and shaking. It was considered by the inmates to be the worst part of the reaper training program.