If there was something missing from Prometheus aside from logic and quasi-competent scientists, it was an alien creature bursting from a human chest. An earlier version of the movie's script involved a particularly bloody encounter with just such a critter. Spoilers ahead.
If you've seen Prometheus, you'll remember that Logan Marshall-Green's none-too-bright archaeologist, Charlie Holloway, sexes up Noomi Rapace's Elizabeth Shaw after becoming infected with the Engineer weapon. In one of writer Jon Spaihts' earlier drafts of the script, Holloway experiences a violent coitus interruptus when a creatures shoots its tentacles out of his chest. This guy looks like a cousin to the tentacle creature pulled out of Shaw's womb. Apparently, xenomorphs aren't the only Engineer beasties who invade that particular part of the human body.