> Really, nothing in between those two? Well the first thing that came to my mind when reading the title was the phenomena of moving rocks in Nevada [1]. It co

> Really, nothing in between those two? Well the first thing that came to my mind when reading the title was the phenomena of moving rocks in Nevada [1]. It could be similar but unlike them this doesn't seem to leave any trails. [1] http://en.wikipedia.org/wiki/Sailing_stone http://en.wikipedia.org/wiki/Sailing_stone