Original: The poisons referred to are usually hydrogen cyanide (HCN), and its chemicals made from hydrogen cyanide, like potassium cyanide (KCN), and sodium cyanide (NaCN).
Simplified: The poisons referred to are usually hydrogen cyanide (HCN), and the chemicals which are similar to it, like potassium cyanide (KCN), and sodium cyanide (NaCN).