Question

why is the em dash used in the following excerpt from gilmans the yellow wallpaper? john is a physician, and perhaps—(i would not say it to a living soul, of course, but this is dead paper and a great relief to my mind)—perhaps that is one reason i do not get well faster. to indicate a change in thought to clarify the meaning of a word to introduce a list of items to explain a concept

Explanation:

The em - dash in the text shows a shift in the writer's thinking, like moving from talking about John to the relief of the dead paper.

Answer:

to indicate a change in thought