Something is considered a poison if it can harm or kill a person if used incorrectly, in the wrong amount, for the wrong person, or by the wrong method. The document discusses two particularly toxic poisons: arsenic, which can be found naturally in rocks and groundwater; and cyanide, which is used for mining and manufacturing and can be produced when some materials burn. Both poisons are very dangerous, even in small amounts, and can cause rapid death through suffocation or organ damage.