Christopher describes scientific mysteries as problems that have yet to be solved. Christopher says ghosts are only a mystery because we do not know the science behind them, but one day we will. He talks about the seemingly random number of frogs in the pond at school from year to year and notes that a formula, discovered by a group of scientists, shows that the population density of frogs runs in predictable cycles that only appear random. Christopher concludes that sometimes complex problems follow simple rules, and that whole populations can die out for no reason other than the way the numbers work.