What is the string of varied thoughts that the mark on the wall stimulates in the author’s mind?

The mark on the wall stimulates various thoughts in the author’s mind and hence can be seen as a perfect example of ‘stream of Consciousness. At first, she thinks of it as a result of a nail but then while rejecting this idea she starts to think about the personalities of the previous occupants of the house. Then thinking about the hole as an ink mark and not a hole she starts to philosophize about the idea of death. Again, she changes her interpretation and sees the mark as just a shadow while pondering over the writings of Shakespeare and the art character composition.