[Quix]

There's always been a percentage hoaxed.

The plant node and other 'scientific' analyses seem to indicate there's plenty that are unexplainable by normal means.

Then there's the cases of them being seen being formed by glowing orbs etc.

[RoughDobermann]

there's plenty that are unexplainable by normal means.

Or by normal people....

[discostu]

The closest these things ever come to being unexplained is that the true believers insist humans couldn't possibly make the really good ones. For some reason they insist people can't possibly make a perfect circle over 100 feet long, the Superdome not withstanding.