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.
Coarse crackles are discontinuous, brief, popping lung sounds. Compared to fine crackles they are louder, lower in pitch and last longer. They have also been described as a bubbling sound. You can simulate this sound by rolling strands of hair between your fingers near your ear.