People have always written about star jelly, a gooey substance that appears after meteor showers or sightings of comets. When people are wandering through the woods, or across their lawns, and see some unidentified goo, they generally think, "Ew. Don't step on that. Someone probably just puked it up." When they see it after the news of a major meteor shower they think, "It fell from the stars!"
It did not, of course, fall from the stars. The most famous case of "star jelly" happened in 1979. Sybil Christian was out one morning, walking around her home outside of Dallas, Texas. She saw strange purple lumps of goo, some of them quite large, with small flecks of metal inside. She alerted her community, and the national press picked it up. It wasn't long until people came to investigate the star jelly. The metal in the goo was lead. Could they be from an alien craft, people wondered? They kept wondering until they drove around and found a battery treatment plant in the area. The purple jelly was caustic soda, meant to wear away the useless materials in the batteries to allow workers at the plant to retrieve re-usable metals.
Other people mistake the various goos, oozes, and foams put out by slime molds for star jelly. Slime molds used to be considered fungi, and some people still think they are. Slime molds, however, lack fungi's structure. They are simply an aggregation of protoplasm or slime. These aptly-named beings eventually decide it's time to reproduce, and start the process of fructification. Fructification means putting out spores, which for slime molds means creating especially light and airy slime. The slime can be yellow, green, or white, and appears to have either bubbled up from the ground (as slime molds are rarely noticeable) or dropped out of the sky.
What's the most likely source of star jelly? When you see a lump of slime and draw back in disgust, your first thought is probably right — someone did puke on your lawn. Analysts at the Natural History Museum in London have determined that a lot of star jelly is frog spawn. The spawn should be in the water, but the jelly found on lawns got gobbled up by magpies. The magpies overindulged and horked the spawn back up on some poor person's lawn. It really is partially-digested puke.
[Via Space Blobs, Straight Dope, Slime Molds]
Top image: James Lindsey's Ecology of Commanster Site.