Maybe the design choice of allowing the lock to be overridden outside of the computer, but the decision itself is a heat of the moment thing from the captain, who feels it's his fault, and Ash's entire objective is to get the Facehugger on board. Or maybe instead how the Xenomorph grew up so goddamn fast.

[quote]In Alien where they bring that dipshit with a facehugger onto the ship.[/quote] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^