i noticed it a couple years ago - its definately NOT on opening - the opening to the back of his throat is shaped like a, ahem, vagina - like harrigan's name for the predator. whats there is another appendage - its forked, and has texture to it - its not just a the hole, which tapers to a point towards the top. not seeing it in other scenes probably has more to do with what mechanics/animatronics they were able to fit inside the hero head with or without the actor's head inside, rather than what the true biology was supposed to be. its something thats actually moving up and towards the back of the throat.