I wouldn't worry. As anyone who has dismantled technology can tell you, usually anything up to 90% of the small screws in any piece of equipment are entirely unnecessary, and in many cases seem to have manifested themselves spontaneously out of the vacuum. Or possibly the hoover.
According to the article it's "In the foreground, near the bottom of the image." I do see something near the bottom, halfway in the gap between the rover, that looks grey.... maybe metallic.
This was taken from http://www.universetoday.com/97774/curiosity-finds-something...
[1] http://www.reddit.com/r/science/comments/116q6s/curiosity_fi...