I know for a fact the first UFOs reported in modern times, just before the crash at Roswell, were boomerang shaped and were reported as 'flying saucers' to describe the motion of their flight, like a saucer skipping over water. Yet immediately after, people saw and photographed saucer-shaped objects. Boomerang-shaped objects were rarely seen. Now people mostly report seeing large triangles instead of discs or boomerangs, because that is what they are told to expect to see.