Graham Hess: Swing away Merrill. Merrill... swing away.
Graham Hess: Everybody in this family needs to just calm down and eat some fruit or something.
Bo: There's a monster outside my room, can I have a glass of water?
Merrill: Move children! Vámanos.
Merrill: Move, children. Vamanos.
Officer Caroline: Merrill... how's work at the gas station?
Merrill: Stimulating.
Graham Hess: What are you thinking about?
Bo: Why do you talk to Mom when you're by yourself?
Graham Hess: Makes me feel better.
Bo: Does she ever answer back?
Graham Hess: No.
Bo: She never answers me either.
Graham Hess: It's happening.
Morgan: I think God did it.
Graham Hess: We're going to board up every window in this house.
Merrill: How do you know boards will do anything?
Graham Hess: Because they seem to have trouble with pantry doors.
Merrill: Everything has a weakness.
Graham Hess: My vote counts as two.
Morgan: That's bullshit. You're cheating.
Graham Hess: Morgan, calm down.
Morgan: We don't know anything yet.
Merrill: Hey, you guys okay?
Morgan: Some guy had a sign saying it was the end of the world.
Merrill: Don't worry.
Morgan: You won't let anything happen to us, right?
Merrill: No way.
Morgan: I wish you were my dad.
Merrill: What did you say? Don't you ever say anything like that again. Ever.
Graham Hess: I don't want any of you spending time with Tracy Abernathy alone. Understand?
Merrill: It's like War of the Worlds.
Morgan: They said there are one of two outcomes of an invasion. One: they fight, and are defeated, and have to return again with full forces hundreds or even thousands of years later.
Graham Hess: What's two?
Morgan: They win.
Graham Hess: The police are here. I am with them. I am a police officer. I just want to talk with you. We know all about the hoax. We already took some of your friends downtown in a paddy wagon. Just tell us your name and why you did it, and we'll give you the same deal we gave the others. Don't throw your life away, son.
Morgan: It's not contaminated, you don't even know what that word means.
Morgan: If you're gonna make fun of it, then forget it.
Bo: This is serious.
Graham Hess: I don't know what got into me.
Morgan: There are pictures. Dr. Bimbu, one of the authors of the book.
Graham Hess: Bimbu?
Morgan: Dad.
Graham Hess: I just asked his name.
Morgan: You had a tone.
Merrill: The nerds were right.
Answer: It's left unclear, though the film proposes several possible theories, and there are other possible explanations as well. One major theory brought up in the film is that the aliens were there to acquire Earth's resources after using up their own. Another theory proposed at the end of the movie is that the aliens wanted humans for whatever reason, as a radio DJ mentions seeing his friend's family being dragged away. There is also a very popular fan theory that the aliens are supposed to represent demons that are merely there to create chaos and test the moral strength of humanity, as the film is ultimately about Graham losing and then regaining his faith, although this is more subtext than anything and may not be literally true.