I always thought that the huge room with a hanging engine (where you find a hacker tool) is the first actual encounter with an Alien which can hunt and kill you. But it appeared that it's already there after the cutscene with Axel's death.

As someone said on a forum: "I waited in the train and it dropped down, I never pressed the "NOPE" button quite so hard in my life"

Oh, there's already a video of it on youtube. Okay, here's another.