At first glance, there is no phenomenon creepier than crop circles - huge geometric designs that appear in fields overnight seemingly without cause, explanation or reason. UFO enthusiasts are quick to supply all three, by attributing the patterns to alien visitors seeking to communicate with humans, using laser beams or other advanced technology to flatten the crops. These fanciful claims can fortunately be dismissed thanks to two quite mundane observations. Firstly, ordinary Earth-born individuals have repeatedly demonstrated how to produce the effects with nothing more elaborate than a rope and a plank. Secondly, there is a clear parallel for the phenomenon in the form of urban graffiti. Sneaking into fields to make crop circles is simply a rural variation of a widespread and well-documented human urge.