What metaphors are used in The Art of the Personal Essay: An Anthology from the Classical Era to the Present by Phillip Lopate?

The author notes that writer, Richard Selzer, is willing to write about his feelings in addition to his knowledge. Selzer is a practicing surgeon. "The Knife" is Selzer's essay and the connection between Selzer's surgical training and his desire to convey his feelings are shown here. In this he talks about the different metaphors that can be used for a surgical knife and the way that it contradicts itself.