Exploding manure terrorizes America's hog farms

The manure pits on pig farms across the United States have been invaded by a mysterious foam—at Ars Technica, Brandon Keim describes it as "a gelatinous goop that resembles melted brown Nerf". It's probably the byproduct of some kind of biological process, though nobody knows exactly what. The larger problem, though, is that the foam is rather explosive.