Cobalt diselenide was a biogenic weapon that affected the nervous system; while deadly to Cardassians, it was harmless to most other humanoids. The agent could be synthesized from selenium and rhodium nitrite, and was required to be kept at a low temperature. Only selenium and rhodium nitrate were mentioned in the concoction of this substance. In the real world, CoSe2 is a non-volatile crystalline solid – its toxicity is not currently known. Zhang et al. describe its synthesis and characterization in Materials Resarch Bulletin, 2000, 35, 2403-8. [1]