Slow as molasses isn’t just a saying—the byproduct of sugar production is usually sticky and viscous, even at room temperature. So historians and scientists have long been stumped by Boston's 1919 Great Molasses Flood.

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Though an anarchist terrorist attack was first blamed for the calamity, investigators soon pointed at the holding tank’s shoddy construction. But the question has remained, why did the molasses explode as a wave and not just slowly drip out of the tank? A group of students at Harvard investigated the event and presented their conclusions at recent meeting of the American Physical Society.