I always think "what is it" when something in the Mars photos doesn't look like rock or sand - because rock and sand is all that is supposed to be there, according to the "science" regarding Mars! So, in a below posted pic is some sort of squiggly stuff beneath and in the shadows of a rock - looks kinda odd doncha think?!!
Rover Curiosity Sol day 1033
http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=1033MR0045210450304204E01_DXXX&s=1033
(http://s32.postimg.org/qln5djqit/Screen_Shot_2016_05_08_at_9_58_05_PM.jpg)
Odd, yes, but not impossible as a result of common geological processes. :)