Seen it twice. One of my favorite movies and by far some of the best digital/graphic set-ups I have seen in a movie so far.

IMO MP, you're reading WAYYY too much into it. It's a movie, it's fantasy, and it's sci-fi. That makes any of the 'logic' irrelevant and pointless because they can do whatever they want because it does not have to be logical in any way. Basically what pfan said, stop trying to pick apart a movie like it's supposed to be a real life situation. They can make they're creatures however they want to and it doesn't have to be based off of anything.

If you don't like true fantasy, then don't watch the movie. I hate when people go to relatively good movies that they know they're not interested in (the genre) and they purposely find more reasons to hate it. Go watch something else!