Chinese worry balls were a reputed form of stress-relief, originating from the region of China on Earth. They were small, tangerine-sized brass balls that, when grinded in the palm of the hand, were supposed to create feelings of relaxation.
Three million years later, the mechanoid Kryten diagnosed the hard-light hologram Arnold Rimmer with a stress-related nervous disorder, and gave Rimmer some Chinese worry balls to help with the condition. When appraising their grave supply situation, and realising that they had go aboard the wreck of the earlier-defeated Simulant Battle Cruiser, Kryten said to Rimmer "after you with the balls Sir..."
When the boys from the Dwarf finally found him on Rimmerworld, Rimmer had been locked away in a dungeon by an army of his own clones for centuries. Rimmer had ground the Chinese worry balls down to about a quarter of the size during that time. (RD: Rimmerworld)