[Dolemite]

Quote:

Originally Posted by En Sabah Nerd

The key word I used in my first post was "necessary." While I generally buy that humans and yautja normally exist in different atmosphere types there's no evidence that one is actually lethal to the opposite species. Predators (the movie) depicts a predator left in the open for hours without a mask on while the humans give no complaints regarding the air so in that scenario it's evident that the two can generally coexist for extended periods without the predator biomasks.

Oh, I think that's made pretty clear in the movies as well. It seems that whatever the Predators breathe is similar to what humans breathe...similar enough that they can get by without their Bio-Masks if need be, but different enough that that they still need a little "boost" here and there when mask-less. Earth air certainly doesn't appear lethal at all to Predators, at any rate.