There is a very poisonous gas out there, with a chemical composition similar to that of carbon dioxide. Carbon dioxide has one carbon atom and two oxygen atoms. Carbon monoxide has one carbon atom and ONE oxygen atom. When carbon monoxide is absorbed into the blood stream, it combines with the hemoglobin in much the same manner as diatomic oxygen (O2) does, but crowds out the hemoglobin’s capability to carry oxygen, and the organism dies of oxygen starvation, silently and with few warning signs other than a splitting headache.
In the illiteracy about chemical compounds that most of the educationally underserved bandy about, the confusion between CO2 and CO is highly probable. One is good, the3 other is bad for people.
CO2 is actually a poison too, but only in amounts around a few percent or more. This is what a lot of people think made the air unbreathable in the movie Avatar. We don’t exactly have to worry about that, though.