Cigarette smoke contains far more tar than nicotine, and tar will deposit on most-any surface (at ambient temperatures), so it's parsimonious to proceed with the "mostly tar" explanation
The economics of tobacco: what education and income tell us about smoking Data released this summer by the U.S
For the hand-rollers and the pipe smokers, you will surely have experience with your loose tobacco tending to begin drying up the moment you open its packaging
(eds) Bethesda, MD: National Institutes of Health Thun M, Day-Lally C, Myers D, Calle E, Flanders W, Zhu B, Namboodiri M, Heath CJ
These interruptions, known as apneas, can last for 10 seconds to several minutes and can occur hundreds of times throughout the night