I have a theory. I have actually been thinking about it for some time. It is nearly impossible to absorb all of the THC from the smoke you inhale. What ever comes in contact with the walls of your lungs (but not all of the smoke comes in contact with the walls, because we exhale the smoke after we feel that it is time to) are absorbed by the right pulmonary vein in the lungs, which then leads to the right atrium, I do believe. With that being said, all THC from a hit can never all be absorbed entirely, unless you take a ghost hit. If anyone wants, I'll tell you about another theory of mine.