The circles appear within a very short period of time. The best estimate I have seen between creation and observation of a circle is within an hour. In some cases a warbling sound and a moving orange light precede the circle appearance. Other cases cited a whooshing sound. The affected crops are bent in a more nearly horizontal position and continue to grow in that position for a considerable time after the circle manifestation.
Microscopic examination shows no fracturing or breaking of plant cells indicative of forced bending.
We have a multiplicity of facts to consider which, when taken together, show a most interesting hypothesis as to a probable cause. Before going into the hypothesis, let me first state that circular patterns have been associated with UFO sightings for many years before Man began launching rockets and satellites into space. A specific case is that of Billy Meier in Switzerland. Videotapes of the patterns left at alleged landing sights have three primary features which correlate exactly with the crop circles. Prior to the last 3 to 5 years, no UFO trace landing site had shown evidence of any pattern beyond simple circles.