Taken by Navcam Left B on-board NASA’s Mars Curiosity rover on 29 January 2016 (Sol 1237), this image shows an object that looks either like a worm or some kind of threaded artefact like a screw or bolt.
It appears the object was uncovered by the rover’s activity in the area. Taking into account the sense of scale given by the part of the rover that can be seen in the bottom right of the image the object appears to be rather small.
Original NASA source: https://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=NLB_507300229EDR_F0521162NCAM00322M_
Is this a sign of current life on Mars?