swamp gas

Etymology

 * So called because it is often emitted from wetlands such as swamps as a result of anaerobic bacteria, and is responsible for their foul “rotten egg” odor.
 * An explanation given by then-skeptic J. Allen Hynek for an alleged UFO sighting in Michigan near Lake Huron in 1966.

Noun

 * 1)  gases emitted from a swamp
 * 2)  hydrogen sulfide
 * 3)  a skeptical explanation to debunk a UFO sighting that a believer regards as silly, illogical or disingenuous
 * 1)  a skeptical explanation to debunk a UFO sighting that a believer regards as silly, illogical or disingenuous
 * 1)  a skeptical explanation to debunk a UFO sighting that a believer regards as silly, illogical or disingenuous