The Washington Post ran this interesting story about something scientists have noticed in the latest series of rover pictures:

The composite image revealed a mysterious substance right at the rover's feet, which scientists described as a "strangely cohesive" clay-like material with alien textures. Spirit exposed the material when it dragged its collapsed air bags across the Martian surface to retract them after its Saturday night bounce-down.

The great thing about a rover, of course, is nothing's out of reach. Assuming it stands up and can move (likely), expect sample reports shortly.