What are opinions on who makes crop circles?
The previous is half correct. The crop circles are too complicated and intricate to be made with a few planks of wood. The hoax circles are terribly made and take too long to make (most real circles appear over night). However, just because they are so well made and so difficult to reproduce (not impossible, it would just require massive complicated machinery), it does not mean they are made by demons. More than likely it means that they are made by superior, highly intelligent beings.
