Well, I guess the pyramids of Giza never existed before Pythagoras was born, nor was the Earth, moon and Sun spherical, nor was Stonehenge arranged in a pattern, prehistoric people didn't paint geometric shapes in caves, and snowflakes don't display geometric patterns. Sheesh, where would we be without the Greeks!

This is easy. Witnesses were using a thing called analogy. They weren't saying the smell was sulphur, they were saying it smelled like sulphur. The periodic table of elements isn't limited to Earth -- we have sent probes to other planets in the solar system and analysed chemicals and minerals there, afterall. ;-)

Anyways, have a read and post your thoughts. It's a very unconvincing argument, but I do agree that many UFO encounters don't fit the nuts-and-bolts pattern and what we consider to be the "norm" here on Earth. The author could have saved some of their argument by including a little of Jacques Vallee's work to debunk the ETV theory. But I just don't buy the argument that UFOs must fit human preconceptions and knowledge -- we barely know anything about the world we live, let alone thinking we know about alien civilisations whom we don't know anything about.

Many researchs insist on a one-theory-fits-all for the UFO phenomena (saying they're all dimensional or they're all natural or they're all nuts-and-bolts ETVs from other planets). There's enough room in UFO reports to fit all theories -- natural phenomena, man-made, supernatural, nuts-and-bolts from outer space, extradimensional, etc. Each UFO encounter must be taken on its individual merits, rather than being forced into a preconceived one-size-only theory. As Stanton Friedman says, some UFOs do display natural or man-made or dimensional or supernatural properties -- but he's only interested in the nuts-and-bolts ones.