From what it seems, you really need to understand a lot about the spirituality aspect of things to understand the nature of a reptilian. Last year, when I was introduced to David Icke, and the other leaders in the the expose of global conspiracy, like Alex Jones, and other guys like him, I was only interested in secrets of the dollar, and the freemasons, and the templars and all that stuff. After reading the biggest secret which I've taken my sweet ass time with(I'm a slow reader, and I don't read it everyday inorder to digest the dense information), after reading it, I've really been captivated by the spirituality side of the material.
When David Icke refers to the 4th dimension, he doesn't mean the scientific 4th dimension, as in space-time, he literally means another plane of consciousness higher than ours. The brain is a perfect cross between science and spirit, and the reptilians have risen to a higher plane of existence than we have. Each plane of existence has different levels of frequencies which your body resonates, and everything I've read regarding these new-age spiritual Ideals, which do seem to be far more old-age than anything, involve entities from higher planes of existence. People don't see these reptoids because their minds are not vibrating at a frequency which allows them to contact 4th dimensional beings. Left-brain technology, like video cameras, couldn't attain video of these beings because they are machine, and are non-spiritual.
However, like David Icke says, which seems to receive much ridicule, is that when the reptoids drink blue-eyed, blonde-haired blood they shapeshift and can stay in the 3rd dimension which is when people see them. But for the most part, they operate from a higher plane of consciousness in which they are trapped because the fear and manipulation has disallowed them to further expansion. To learn more about the dimensional stuff, and planes of existence, check out some of the books by Bob Frissell. I'm reading his 3rd book right now. They're short and easy reads, I highly suggest them.