In Chapter 11 of To Kill a Mockingbird, upon seeing Mrs. Dubose in bed, Scout describes the scene.
I wondered if Jem's activities had put her there, and for a moment I felt sorry for her. She was lying under a pile of quilts and almost looked friendly.
Scout also notices a syringe, a teaspoon, and some cotton on the washstand by Mrs. Dubose's bed. When Jem defends Scout after Mrs. Dubose calls her dirty, Scout expects a rant, but Mrs. Dubose just tells Jem to start reading. Mrs. Dubose then asks the kids to move closer.
Then the kids get a better look. Mrs. Dubose looks sickly, old, and, contrary to her usual commanding demeanor, feeble.
She was horrible. Her face was the color of a dirty pillowcase, and the corners of her mouth glistened with wet, which inched like a glacier down the deep grooves enclosing her chin.
At one point, Scout notices that Mrs. Dubose starts to have a kind of fit where her mouth seems to "have a private existence of its own." Atticus later tells her that people who are sick can not control themselves at times. Despite being made aware that Mrs. Dubose was sick, Jem is still surprised when he later finds out that she has died.
What is significant about this event in the novel is that the children see a different side to Mrs. Dubose. Rather than seeing her as a vile, contemptuous old woman, they see her as a needy, feeble person; someone Atticus considers to be one of the bravest people he's ever known. This is part of the ongoing lesson of considering the many aspects of other people's lives.