Umm...what the heck did Curiosity just find on Mars? My imagination is running wild and I am entirely dismissing the possibility that it's a piece of metal from the Rover itself this time.
Now the rover has imaged a small metallic-looking protuberance on a rock. The protuberance appears to have a high albedo and even projects a shadow on the rock below. The image was taken with the right Mastcam on Curiosity on Sol 173 — January 30, 2013 here on Earth.