Well, yes, my mind did perceive a familiar shape when I saw the picture, but I am not so sure about it being vague or random. Somehow that explanation causes me to think of the statement, “Just because I’m paranoid doesn’t mean they aren’t out to get me.”
It seems to me, ‘Pareidolia’ is in this case a useless term. It has very little to do with anything. Our minds perceive the image because the image looks like something we have seen before. In this case, the rock looks like a rat. Either that, or there is a dead rat on the surface of Mars. That image isn’t vague and it isn’t random. It looks like a rat.