I just may have figured it out...hopefully. When i disturbed him to get the latest pic, he went and wedged himself (tightly) between the background ( a styrofom rock-like background that came with the exo terra) and the top metal screen. I noticed bright green markings where his skin is in conntact with the screen, much like the very first pic in this thread. Perhaps he wedges himself so tightly that circulation is cut off or maybe just rubbing occurs. Maybe the frogs skin is delicate enough to be effected by this. I blocked the space where he wedges himself with paper towel. We'll see if that helps.