A medium, Phil Scott, uses a pair of dowsing rods in a crop formation in southern England in August 1991. Dowsers use a rod, stick or pendulum to "divine" a substance or energy, most typically underground water. Crop formations are patterns of flattened plants in crops such as wheat or barley. They started appearing frequently in the mid-1980s in south-west England. Their cause is unknown. Explanations range from the scientific "plasma vortex" theory to suggestions that they are created by alien intelligences. Some people believe an unknown earthly force is involved which can be detected by dowsing. Dowsers claim to distinguish "real" circles from fake ones.