Prisoners deemed too weak to be good workers were sent to the gas chamber. To prevent panic, the Nazis told them they would be taking a shower. Instead, the disguised showerheads gassed the prisoners to death using Zyklon-B pellets. Zyklon B, a poisonous gas made from hydrogen cyanide crystals, was originally manufactured as a strong disinfectant and for pest control. The SS used Zyklon B for mass extermination in the gas chambers in an effort to satisfy Hitler's demand to annihilate all European Jews.