http://simple.wikipedia.org/wiki/Alimentary_canal,
http://www.maryroach.net/gulp.html
Some movies really want to be connected to food-and-shit.
Officially the movie Prometheus isn't suppose to be, shit monsters from outer space, but there are some things do want to get into the stomach & intestines of inspecting victims.
The shit mix of death http://avp.wikia.com/wiki/Black_Liquid
Worms & especially intestinal worms are bad enough, but if they mutate into something stronger, lookout!
The Shitsnake or hammerpede, doesn't just go down the throat of Millburn, it goes through his gastrointestinal_tract. It can feed on the stomach & intestines & then create a nest & lay some eggs. After churning & ripping up the victims guts, the shitsnake goes back up the throat & guards its nest from just inside the mouth. When the rescuers arrive they see the shitsnake pop out of Millburn's mouth to temporarily abandon its nest.
Unlike the shitsnake, the Facehugger isn't interested in getting into the intestines of a victim. G.W._Kane was placed into a temporary coma by a facehugger, but still kept alive instead of being choked to death. Once the facehugger feels that enough time has passed for a new creature to grow inside the victims stomach, it goes off to die. The_Xenomorph creature feeds off the stomach & intestines while its in a Chestburster-shitsnake form, but at a certain point, it wants to escape its nest.
Unless removed from the stomach, the trilobite will eventually fill the abdominal cavity & expand into the intestines. At a certain point the rapidly growing trilobite will burst out of its nest. Although surgically removed & trapped in a room, the trilobite patiently waits as it continues to grow. As soon as the doors are opened the trilobite grabs & wrestles with an Engineer. Eventually the engineer is tired out from all the wrestling & becomes a nest for a new creature known as a Deacon. Eventually after feeding & ripping up the guts of the engineer, the deacon rips out of its nest.
http://io9.com/5916778/the-best-part-of-prometheus-isnt-the-aliens
