While "chewing" is the popular term for it, the leaves should never actually be munched upon. Instead, they should be placed one-by-one into the cheek, forming a small saliva-generating ball which you just leave there. Because the stems of the leaves can hurt the inside of your cheek, you should remove them first. Some remove the stems by sliding the leaves between their two front teeth, while others use a lick-fold-tear method.
Consider a distinctly US American product. Let's say hot dogs, invented in 1870 on Coney Island and enjoyed in our great nation ever since. But in 2015, Korean scientists learn how to distill the noble hot dog into a lethal drug. Hotdogaine. International hot dog trafficking becomes a lucrative business and, over decades, people across Asia become addicted to hotdogaine, even while aw-shucks, overall-wearin' Americans continue to enjoy the hot dog in its "natural" form. You see where I'm going with this?
