A COUPLE of weeks ago I saw a new scientific paper from Clemson University that struck me as both pioneering and hilarious. Accompanied by six graphs, two tables and equations whose terms include “bologna” and “carpet,” it’s a thorough microbiological study of the five-second rule: the idea that if you pick up a dropped piece of food before you can count to five, it’s O.K. to eat it. I first heard about the rule from my then-young children and thought it was just a way of having fun at snack time and lunch. My daughter now tells me that fun...