Mary Roach, a science writer, is one of the few humans who’s tried inhaling Stench Soup. In her 2016 book “Grunt: The Curious Science of Humans at War,” she described the aroma as “Satan on a throne of rotting onions.”

Is Stench Soup really the worst smell in the world? That’s hard to say, in part because researching bad smells can be difficult. Chemists tell cautionary tales about a substance called thioacetone, which in 1889 was the subject of experiments in a lab in Freiberg, Germany. One thioacetone reaction produced a smell so bad that it spilled out of the lab and swept through the city, causing widespread panic and evacuation, along with a lot of people being sick in the streets.