... Really, what is it?
Mars is, on the one hand, a source of unending fascination. It is, after all, Mars. And we're exploring it with, you know, a nuclear-powered robot that leaves Morse code in its tracks. But Mars, on the other hand -- and no offense to it or to said robot -- is also a source of unending ... unendingness. It is dusty and hilly and rocky and red, mile after mile. Lather, rinse, repeat.
Except. Every once in a while -- and there have been several of those "onces" in a not-very-long "while" -- Curiosity happens upon something that is not red, and not dusty, and not necessarily rocky. There was December's "Mars Flower," a pebble-sized white-ish object that some thought to be a fossil, and some thought to be a rock, and some thought to be a piece of errant plastic from Curiosity itself. (The jury is still out on what the object actually is -- though it's pretty safe to say that it is not, in fact, some kind of Martian marigold.)
And now we have another Martian Mystery Object -- this one a thing that looks suspiciously like a hunk of metal. Curiosity detected it, through a high-res image taken from its Mastcam, on Sol 173 (January 30 in Earth days). Universe Today calls the object "a small metallic-looking protuberance" -- it resembles a thick, bent nail, sticking out of the Martian surface -- and it is visible in part because it projects a tiny little shadow on the rock below.