This is a little piece called
I've got some time to kill.This is a theory of how the egg got on board the Sulaco.
I didn't come up with this theory but I have detailed it further.
Things to remember before reading:
- This only takes into account the Assembly Cut of Alien 3.
- The writers of the film never included any of this.
Spoiler
Life's too short.
As the Queen leaves the hive after Ripley has destroyed it, one of the "Royal" facehuggers...
...climbs on her back.
As Ripley, Newt, and Bishop are attending Hicks in the dropship, before they walk out into this shot...
...the Queen lays an emergency egg on top of the Royal facehugger which then carries it off into the hull of the Sulaco. The Royal facehugger is built to carry eggs, like so...
(Egg size is debatable.)
...The only onscreen evidence for these Royal facehuggers carrying eggs is the fact that the eggs are placed all over the ground in the hive (seen in Aliens.)
I am aware that the drones/warriors can carry the eggs, but for the sake of argument these Royal facehuggers can also carry eggs in order to move them to more secretive locations, which is evident in the opening of Alien 3...
So the egg hatches and the facehugger from the egg...
(You can see it's not a Royal facehugger)
...impregnates Ripley causing the fire that ejects the EEV to Fiorina 161. Along for the ride is the Royal facehugger, which impregnates the Ox and is later found by Murphy.
This theory can also be backed up by the sound of the scuttling facehugger at the end of Aliens, after the credits.
For me personally this is how it went down.