Swamp gas.
“Swamp gas.”
There’s an amusing story behind this. J. Allen Hynek, astrophysicist and one of the Project Blue Book investigators, was asked about reported strange sightings in Michigan. Shooting from the hip he said maybe it’s swamp gas. He had no information at that point and had already reviewed literally thousands of reports on sightings so he automatically went for a conventional answer. It sounded like he was annoyed with yet another distraction.
He specifically mentions how he inadvertently created the ‘swamp gas’ legend in his book “The UFO Experience.”