Haven't seen any myself, but they seem to resemble entities that a buddy of mine once told me about seeing while driving on a road. If I remember the story correctly, first he saw some standing by the side of the road watching as he passed by; then, later on, he saw some in the middle of the road and was afraid he might hit them, but they disappeared out of sight as he got closer.

Personally, I don't believe in this kind of stuff, but it can be fun to imagine.