I think you need to go back and better explain why you think seeing an "air hole" under the armpit of a character who's is obviously of an alien species qualifies as a slip up. How do you know that the hole wasn't placed there by the movie's design team as part of the (alien) characters normal anatomy?
Hey Mister Voice! Have you been laughed at lately? Have you wondered why? Is it something to do with those incredibly stupid things that you say? Why would the designers make such a small addition to the costume like an air hole. How retarded do you have to be?
I'm afraid I have to agree with Mr Voice. How can we know for sure that an alien WOULDN'T have some form of hole under their arms, do you you expect aliens to have the exact same anatomy as humans?? Maybe the hole is for processing oxygen, or maybe a self-defense mechanism similar to a squid! In fact...that shouldn't be considered a slip-up, do you realize how overheated you'd be in that outfit if you were completely sealed in it?!?