Donne vs. The Runaway Bunny
Vivian chooses to have Dr. Ashford read The Runaway Bunny to her rather than recite a Donne sonnet. This is a metaphor for how what is most simple in life is most profound and important in the overall scope of our lives.
Dr. Jason
Jason's tact and bedside manner is a metaphor for how the medical community can become sterile in their approach to caring for their patients. That his lack of truly seeing Vivian represents a larger problem that is quite normal in patient care.
Wit
The play itself is a metaphor for what wit is, which as Vivian explains is the personal effort and sacrifice to gain such a deep understanding of something that it becomes simple, seemingly effortless to the one who wields it. Vivian has sacrificed her life to studying poetry, to studying Donne and his wit and by doing so she is able to see the depths of life quite simply as her life is near its end.
Barefoot
Dr. Ashford climbing into bed with Vivian to read her a story is a metaphor for how she has allowed poetry to be learned through her personally experiencing life and the sensations and feelings one must have in order to attain understanding of how to write what they have lived.
Susie
The character of Susie is a metaphor for the personal care and heart within the medical community. She represents specifically the nurses in the medical profession and reveals their commitment to the patient as a human being rather than an experiment.