xkcd illustrator Randall Munroe gave an elaborate answer to the question, “How long would it take for a single person to fill up an entire swimming pool with their own saliva?” as part of his What If? series. The answer compares the time it would take to fill the hypothetical pool to the evolution of human society from prehistoric to modern times.
Munroe tackled similarly absurd questions in his book What If? Serious Scientific Answers to Absurd Hypothetical Questions.
image via What If?