Plus you can always play the "mimic" game. I've got a page or two somewhere in my sketchbook where I was developing spacecraft and air vehicles on the shapes of pre-Cambrian sea creatures and modern crustaceans. I think, when that technique works, you manage to somehow bring some of that intangible "realness" across from the real thing. When it fails, of course, people say "Hey -- that's just a trilobite with air intakes!"