The nine objects Kenneth Arnold said he saw were not saucer-shaped. Drawings showed something more resembling a flying wing style aircraft. However, he described their movement as a kind of skipping, like a saucer skimmed over water. Press reports picked up the "like a saucer" phrase, and reported it as a "flying saucer". George Adamski contributed to the popularity of this term with his books, such as "Flying Saucers Have Landed" (1953).
The number of different shapes, sizes and configurations of claimed UFOs has been large, with detailed descriptions of chevrons, equilateral triangles, spheres, domes, diamonds, shapeless black masses, eggs and cylinders being prevalent. The fact that there are so many different shapes, size and configurations favours the socio-psychological paradigm.
Skeptics say there are indeed genuine sightings of strange flying objects which are usually logically explained. No physical evidence of an alien spacecraft has ever been produced.