Final answer:
Ben Franklin was referring to asparagus when he mentioned that eating a vegetable can cause urine to have a disagreeable smell due to sulfur-containing compounds produced during digestion.
Step-by-step explanation:
The vegetable that Ben Franklin was referring to when he wrote that eating it would give urine a disagreeable odor is asparagus. This phenomenon is due to asparagus containing asparagusic acid, which breaks down into sulfur-containing compounds that are responsible for the characteristic smell in urine of some people who have the genetic trait to detect it.
The science behind this smell involves complex biochemical reactions that occur during digestion. When asparagus is broken down in the body, the asparagusic acid it contains is metabolized into various sulfur-based compounds. These compounds then exit the body through urine, resulting in the unusual smell that Franklin noted.
It should be noted that the ability to smell these compounds in urine after consuming asparagus is genetic, and not everyone can detect it. The phenomenon has intrigued scientists and non-scientists alike, leading to studies on the genetic basis of this sensory experience.