The Zipper
People are always saying you can see the zipper on the monster.
What makes them think the monster is walking around in the nude? He's intelligent, so he comes from an intelligent species. Maybe they invented clothing. Do we think we're the only creatures in the Universe who wear clothes? (That attitude aggravated me in "Close Encounters of the Third Kind" and "E.T.")
I assume the monster is wearing a suit of clothes -- that's what it looks like, anyway, the way it creases when he walks. I also assume they invented zippers on Mars at some point.