Welcome back to "Doggerel," where I ramble on about words and phrases that are misused, abused, or just plain meaningless. Before I continue, I'd like to thank all the commenters for the various compliments and suggestions you've brought me. This dog intends to be man's best fiend.
This particular phrase is a favorite among ufologists and ghost hunters. Despite what they like to think, a human being's eyes are not cameras, and their visual cortex is not an objective piece of film (or memory card, to stay current). There is a lot of things going on in the human mind, and to minimize the workload, biological organisms often take shortcuts. Human beings, for instance, are distinguishible from most animals because they've reduced their sensory load in order to make room for cognition. Though they miss out seeing everything that twitches, very high and low sounds, and other things, they can think more deeply about the stimuli they do receive: A lion seeing a rock rolling down a hill sees only that. One of the early humans could have been inspired by such an event to make a wheel, starting a revolution in their way of life, leading to a day where humans get so much food, obesity is a leading health problem. (This dog needs to lose a few pounds, too, by the way.)
The problem with this increased cognitive ability is that humans often see what they want or expect to see: Human beings live and die by understanding (or misunderstanding) the way the world around them works. Understanding makes them feel good. Unfortunately, the illusion of understanding also makes them feel good. Additionally, much of human understanding comes about in the form of pattern recognition. Scroll up and look at the opening paragraph. See anything wrong? Here's a hint:
That was inspired by a faint memory of a Mr. Wizard episode: The scientific spellcaster was holding a flashcard with the phrase, "Dog is man's best fiend" on it, showing it to the kid guest, who kept saying it read, "Dog is man's best friend." The latter phrase is common enough that the human brain typically doesn't bother looking for deviations like a missing "r." It fills in the missing information based on what's familiar: There's usually no point in me looking at every KFC sign I come across, just to make sure it isn't KEC.
Such is often the case in ufo, ghost, and Bigfoot sightings: These entities are familiar enough in pop culture that a person, given something indistinct enough, could start filling in particular traits in his memory, simply because his brain assumes the visual patterns from fantasy fit into the real situation. Coupled with boundless enthusiasm, it's easy for a gullible human to turn a bright dot in the sky into an intricately detailed sci-fi spacecraft.
This cognitive trouble doesn't end with visual stimuli, either: It applies equally to the auditory sense, and even dreams. Obi-Wan wasn't quite right about your eyes deceiving you: Your own brain can deceive you, even if your eyes are in perfect working order. Be prepared to second guess yourself.