It's not until after she dies that Scout and Jem get a sense of what's going on behind the drool and venom: Mrs. Dubose is a morphine addict who had vowed to go clean before she died, and enlisted Jem and Scout (without their knowledge) to keep her off the stuff for longer and longer periods of time.
http://lungsounds.net/rales-lung-sounds/ - Rales lung sounds are small rattling noises heard around the lung. This happens when air exposes closed air spaces. Rales can be shown as wet, dry and coarse.
The tactile sensation you feel over your chest has the same cause as the sounds one can hear with a stethoscope, mucus or water in the airways or air sacs. Rales are fine crackles and can usually not be felt with your hand. They are most characteristic of heart failure and a class of diseases called interstitial lung disease (ILD). Ronchi are coarser sounds caused by the rattle of mucus in the airways.