The term "per anum," which translates to "by way of the anus," appears in discussions about anatomical and biological functions. This phrasing often relates to various medical or scientific contexts concerning the alimentary canal, as explored by Mary Roach in her book, "Gulp: Adventures on the Alimentary Canal." The nuances of such terminology highlight the complexity of human physiology.

Additionally, the phrase "per annum," noted for its correct spelling with two n's, refers to an annual measure or rate. In a light-hearted manner, Roach addresses the question, "What is the birthrate per anum?" suggesting that the desirable answer should be zero, emphasizing the humorous and insightful approach she takes toward understanding human biology.