Skulls on Mars! OMG!

OK, I've wasted too much time on this post, so I'll try to make it short and sweet... with photos. This story has come across my radar too many times for me to ignore it:
I guess that rock is thought to look like a skull. I was thinking coconut or turd. Which is my point. We are hard wired to recognize patterns, even when they're not there. I see a coconut, someone else sees a skull. In fact, it's a rock. Weathering (particularly in arid and salty environments) can create some very strange forms.
Is this an octopus with it's arms cut off? Or an upside-down mushroom? (hint: it's a rock. pdf alert)
Is this a dragon? or a fossilized pterodactyl? (hint: it's a rock)
Is this a dinosaur skeleton? or a giant sponge? (hint: it's a rock)
Is this a giant worm? or a close up of renaissance neckwear? (hint: it's a rock)

The point is not that these particular rocks are dull and uninteresting. Quite the contrary. First, I don't think there is such a thing as a dull and uninteresting rock if you look closely enough (though repetition can get tedious), and these are particularly interesting in their forms. The point is that we sometimes perceive things that we're not actually seeing: perception requires interpretation. We are not always the best interpreters.

Pictures like the "skull" above have been around since the rovers landed. For a while I participated in an online discussion group, and finally had to quit because it had been entirely taken over by cranks who were literally finding several "skulls" and dozens of "fossils"every day, and the moderator couldn't understand that those of us who wanted to discuss "Serious Science" were offended by the fact that these cranks completely clogged any science discussions with their rants about NASA coverups, Martian Dinosaurs and Birds, and the implications of these "discoveries" for further discoveries of extraterrestrial life.

The most common line of self defense was that "You scientists have been so narrowly trained that you've lost all your imagination and curiosity. You just think you know it all." This from people who want to claim great insight into planetary geology but have never heard of, let alone seen, shatter cones. Now whatever faults and failings I may have, narrowness of training and background knowledge, and a conviction that I know it all, are not among them.

Since I'm tired of being polite, I'll simply respond pre-emptively: if you think a complete lack of knowledge and training in any subject gives you particular insight and credibility in that subject, you are a complete idiot, and should consider quitting your career to become a talk show host.