Grinder screwup?
Some of the recent Opportunity photos, featuring what is probably the next target rock for analysis, show an odd dent in the sand in front of the rover. My call on this dent, a circle with a smaller offset circle inside it, is that it looks a lot like what would happen if you told the RAT to grind a sand pile. Did they miss the rock with their instructions? Or was there some good reason to grind a sand pile?