I was walking along the road-edge of a sidewalk when a mysterious apparition entered my vision at the left, a long thin unidentified object sliding quickly across above my head. It’s amazing what complex analysis our brains perform to enable us to “see”, and we can appreciate it even more when the brain misfires on something that briefly makes no sense. Vision relies heavily on a total world view of our environment and everything we know about, to give us useful images.
I shied away in terror, sure that something was about to land on my head. But as the Volkswagen drove up and past me, I identified the narrow long racing boat that stuck out a good 15 feet in front of the car. Until I could see most of the boat, it was just a UFO.