Mike D’Angelo of the AV Club, on 2001: A Space Odyssey, pretty much my favorite movie ever:

What makes the human beings in 2001 seem a bit less than fully human isn’t just the nature of the performances—it’s that every interaction among them is completely functional. We’re seeing people say and do whatever is required to achieve their objective at that particular moment, and nothing more. HAL, by contrast, demonstrates what we all recognize as neurosis. And while it’s mostly implied by his behavior, it does have one explicit manifestation: that refusal to answer Dullea’s summons for 43 seconds, followed by capitulation when it becomes clear that Dullea isn’t gonna shut up. That’s so human, it almost hurts.