The Yellow Wallpaper

In Part V, the narrator discovers why the wallpaper seems to shake at night. The woman in the wallpaper seizes the bars of the pattern and shakes them as she tries to climb through. Then narrator is not sure if it is only one woman in the wallpaper's pattern crawling around fast, or if there are many women. In the bright spots she is still, and in the darker spots, she shakes the bars of the pattern and tries to climb through. But no one can get through the pattern, which has strangled so many women's heads.