A mysterious foam spread through the streets of a Japanese city on Saturday after two earthquakes struck the country, killing dozens of people, Mashable reports. With pedestrians and drivers in Fukuoka moving through the muck, people posted images of it on Twitter (here and here). One called it "disgusting," the Independent reports, but a downtown resident wasn't too concerned: "People were posting pictures on Twitter and it was near my house, so I went out to have a look," says Kazuki Nabeta. "There was a fire engine there. There wasn't anything special about it—it was normal foam." Some in the southern city say a burst pipe may have unleashed the foam, the Telegraph reports. The quakes, which struck Thursday and Saturday, have killed at least 41 people and injured about 1,500. (More Japan stories.)