In the book "Gulp: Adventures on the Alimentary Canal" by Mary Roach, the author introduces a humorous slang term for the rectum, referring to it as a "prison wallet." This playful expression highlights the often taboo subject of bodily functions while making it more accessible through humor. Roach's work frequently blends science with wit, encouraging readers to engage with subjects they might otherwise find uncomfortable.

The use of such slang illustrates how language can shape our perceptions of anatomy and bodily functions. By adopting a light-hearted approach, Roach invites readers to explore the complexities of the alimentary canal without embarrassment. Her writing shines a light on the curious ways we discuss and understand our bodies, effectively using humor to bridge the gap between the scientific and the personal.