Humans cannot possibly make aliens in films! its impossible.
surely alien is something which is completly and utterly inhuman - yet all the aliens in films seem to have: sight, hearing, tough, smell, two legs, two arms. Yes they may look a little strange with green blemished skin, but overall, they're still very humanistic
to make a real alien you need to think outside the human box
note: i am not saying i can make up an alien ...
... because to do that, surely you would need to forget all that you have ever learnt in a human enviroment, and animal for that matter; and come up with a charater which is completly and utterly origional, it would be totaly unrecognisable to anyone else. then, would you be able to see it?
how would we recognise something that is so unfamilliar and possesses no charactersitics that us human would recognise, however obscure some creatures are. we can recognise animals by eyes, limbs, lungs, movement and behaivour. how would we recognise something so obscure that its characteristics have nothing smilar to what we are used to. would we just overlook it? is there an alien sat right next to you?