When Ripley and crew decide to detonate the Nostromo, Lambert and Parker are sent down one floor to gather coolant. Ripley apparently stays on the same floor and enters the narcissus, before climbing up another floor to reach the bridge.
She's then seen going down one floor when Parker is being killed, and continues from there down a hallway during Lamberts death. At which point, she is only about 20 feet or less from the room where they were killed, and arrives at the doorway less than 5 seconds after lambert dies. The alien is gone. She retreats down another hallway and activates the self destruct, and in the directors cut, go down another floor into the hive.
She then goes up another floor, where she runs into the alien, who is blocking her way to the narcissus. Likely, this was the "suitcase" scene where the alien was curled up on the floor. She retreats back down the hall and goes down another floor to stop the self destruct, while chap apparently goes into the narcissus. Then she goes up again, gets jones and escapes.
So, after it killed lambert, it apparently got out of the room in less than 5 seconds and was next seen one floor above, blocking the way to the narcissus.
So, did it know Ripley was armed and just ran away? Was it so preoccupied with lambert that once it killed her it instantly went up to find ripley (where it believed she still was) not realizing she'd already come down? Was it sitting there confused and trying to locate her or something when she startled it? Or was it legitimately intelligent enough to immediately cut off the escape route for the remaining host?
What was it doing? Where was it going?
Any theories or thoughts?