The brain responds to this "reward" by developing a very strong primitive response which is nicotine addiction
This includes not causing discomfort to them by the foul smell of our mouth, body odor, clothes, etc
The authors, post-hoc, unsuccessfully defended tossing out 27,000 ever vapers by inventing a chemical exposureleading to molecular changes sometime in their entire life. But they kept in their study people who smoked up to 100 cigarettes a far more toxic product
Eros and Civilization: A Philosophical Inquiry into Freud
Depending on the source, the residue may include nicotine, tar, oils, grease, resins, and combustion byproducts
But markets rarely respond in straight lines