Crop Circles

One of the most prevalent and insidious informal logical fallacies is the argument from personal incredulity: I personally can't explain x, therefore the explanation must be y (and y usually takes the form of God or aliens or ghosts, or some other arbitrarily chosen being). You should never take your own epistemic, cognitive and imaginative limitations as evidence of anything other than your own epistemic, cognitive and imaginative limitations...

When people can't imagine how ancient Egyptians could have built the pyramids, for instance, their minds almost immediately go to aliens. It's worth remembering, however, that monuments like Stonehenge could be built by a single person with some primitive tools and lots of ingenuity, so when you have thousands of slaves, pyramids are a piece of cake.

So, when during the 70's, crop circles started appearing in rural England (and subsequently in other parts of the world), it should come as no surprise that many people took them to be proof of extraterrestrial intelligence visiting us (because when civilizations advanced enough to travel through the vastness of time-space need to communicate important messages to us, they do in wheat while no one can see them).

Tellingly, no messages actually appeared (other than a few vague passages about world peace and nuclear disarmament). When people thought that aliens would use the language of mathematics to communicate with us, the mathematical symbols drawn never superseded any mathematical knowledge that wasn't already available to human mathematicians, and only after mathematicians made new discoveries would such discoveries 'magically' start appearing. In the following clip, Stephen Fry gets into the silliness of this phenomenon.

What people don't get is that it wasn't aliens... it was the chupacabra :)