'Normally, I see rocks as rocks,' said one commenter, 'This can't be a thigh bone, can it?'
More than two years into the Curiosity rover's lonely trek across Mars, conspiracy theorists believe they have struck gold: an 'alien thigh bone' has been spotted on the surface of the red planet.
For keen alien hunters, the image above - taken by the rover's MastCam on August 14 – is proof that large animals once roamed Mars, possibly even dinosaurs.
"Simply put this shows that there were some living things on the Mars (sic)," asserts an anonymous editorial writer at Northern Voices Online, while the popular site UFO Blogger compares the find to previous images of a "fossilized, reptilian spine" and a "human finger".
The regularity of these 'finds' is of course testament not to the once-flourishing wildlife of Mars, but to the human brain's remarkable capacity to spot patterns in random noise.
This was a handy trait for our ancestors when identifying a potential predator among the primeval foliage, but in modern times it's more likely to lead only to those little 'huh' moments when we spot a face in some inanimate object.
Of course, there is some truth to conspiracy theorists' hopes of life on Mars, with scientists pointing out last year that the asteroid impact that killed of the dinosaurs could have flung rocks carrying organic matter to the red planet some 66 million years ago.
Unfortunately, at this point (and for roughly 3 billion years prior) Mars was a barren place with no flowing water. However, if the microorganisms from Earth had hitched a ride to somewhere a little more hospitable, like Europa then it could be a different matter altogether.