NASA – Odd Mars Rover Mast Image (mars.nasa.gov)

Wasn't me; I saw this link in my "Science News" app feed about 15hrs ago, was just a link and title that said "Mars Photo - Anyone [see] this, and can explain what it is?"

I thought it was pretty amazingly symmetric, but this tadpole-shaped rock looks like it could be sculpted by wind or water flow.

I'm not a geologist, but I know a bit about hydrodynamic. The Karmen Vortex Street (KVS) [1] is generated in the trailing flow arount a blunt object. I've also seen videos of a dead pike fish tethered to a blunt object in a flow and the fish shape self-aligns to the flow so well that the dead fish actually starts to "swim" upstream against the flow. Fish shapes and KVS's are related.

I guess my hypothesis would be that this tadpole like shape could have been formed by a persistent KVS flow.

However, it looks like a toy model that some little green person sat down there:)

1. https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_vortex_street....