Under the right conditions, hot water can freeze faster than cold water

In 1963, Tanzanian student Erasto Mpemba noticed his hot ice-cream mix froze before a classmate's cooler mix, and was mocked by his teacher for claiming it. He later teamed up with physicist Denis Osborne, whose experiments confirmed hotter water could indeed freeze first under certain conditions, published together in 1969. Aristotle and Descartes had noted similar effects centuries earlier, but it still lacks one settled explanation, and depends heavily on exact conditions.

— Erasto B. Mpemba, Denis G. Osborne, Cool? — Physics Education, 1969