If you like history or just enjoy trivia facts, you've probably heard of the Great Molasses Flood of 1919—the Boston disaster where a giant tank holding molasses burst and killed 21 people. Many people, upon learning this, find it kind of funny. How can you not outrun molasses? The speed at which the viscous, sugary substance flows literally gave rise to the phrase "slow as molasses."
Well, as Atlas Obscura will teach you in less than four minutes (with some amazing, haunting photos this author had never seen before), all that changes when you put 2.3 million tons of the stuff in a tank that's too small and too thinly walled to hold it. Why was it so unsafe? Because the owners of the giant molasses tank were trying to make rum before Prohibition went into effect, so they ignored the night watchmen who said it "groaned" constantly, and painted it brown to hide the leakage:
It obliterated elevated train tracks, sent steel shards flying for blocks, and the pressure fired the rivets holding the tank together out in every direction like bullets. The thickness of the substance meant that struggling in it only pulled you down further, like sticky quicksand. The initial wall of goop was two stories high—it burst into windows (and basement apartments) and drowned people who had no chance to escape. It was, in short, not very funny.