Ever since the days of Aristotle, people have made the counterintuitive observation that hot water sometimes freezes faster than cold water. In modern times, the observation has been named the Mpemba effect after Erasto Mpemba, an elementary school student living in what is now Tanzania in the early ’60s. When making ice cream, Mpemba observed that using warmer milk causes the ice cream to freeze faster than when using colder milk.