I remember some years ago when me and my brother was watching a moviec called "Reign of fire, a movie about dragons. The movie itself was crap, but the dragon-part led to an interesting discussion we still don't agree fully on. Basically the dragons in the movie was pretty much big, flying, firebreathing lizards with no forearms. They only had the rear feet and wings. My brother accepted them as dragons right away, but I'm used to the "traditional" dragons and hated them. We started arguing if the creatures in the movie could be called dragons or not, and we both had arguments for and against. He said dragons don't exist, so you can make a flying hamster and call it a dragon if you want to. If dragons don't exist anyway, the flying hamsters will be your version of a dragon. I argued that dragons don't exist in -this- world, but they do exist in our culture, myths, legends and stories. In short, they are so commonly known that if you say the word "dragon" to someone, they will usually know exactly what you are talking about. If I say "little grey men", what do you think about? Most will think small, humanoid creatures with big, black eyes, no hair, small mouths and all that. It's commonly accepted that that's what aliens, or little grey men if you wish, look like. But they don't exist, so "little grey men" could just as well be short, normal humans with grey skin. They would technically be little, grey and men, after all. So the question is thus: How much can we change commonly known fantasy-creatures like dragons, fairies, elves, mermaids etc and get away with it?