Graham Hess: Isabel, you are going to feel very silly when this turns out to be make-believe.
Tracy Abernathy: I swore 37 times in the last month. I said the 'f-word' a couple of times, but it was mostly 'shit's and 'bastard's. Is 'douche bag' a curse?
Graham Hess: I suppose it would depend on its usage.
Tracy Abernathy: How about "John you're a douche bag for kissing Barbara"?
Graham Hess: It's a curse.
Tracy Abernathy: Oh, well then it's not 37 times it's 71 times.
Colleen: Tell Morgan to play games, it's okay to be silly.
Graham Hess: I will.
Colleen: Tell Bo to listen to her brother. He'll always take care of her.
Graham Hess: I will.
Colleen: And tell Graham.
Graham Hess: I'm here.
Colleen: Tell Graham... see. Tell him to see. And tell Merrill to swing away.
Graham Hess: See this is why we're not watching TV, people become obsessed.
Graham Hess: You're scaring your sister.
Bo: I'm already scared.
Officer Caroline: What kind of a machine bends a stalk of corn without breaking it?
Graham Hess: It can't be by hand, it's too perfect.
Bo: Are you in my dream too?
Merrill: There are a lot of things I can take, and some things I can't. But what I can't take is when my older brother, who's everything that I want to be, starts losing faith in things. I saw that look in your eyes last night. I don't ever want to see that look in your eyes again.
Graham Hess: There is no-one looking out for us. We are all alone.
Ray Reddy: Don't open my pantry, Father. I found one of them in there and I locked him in.
Caroline: Old Mrs. Kendleman twisted her ankle, as she puts it, diving for her life when a bunch of school kids rode down the sidewalk on skateboards. She went down to Thornton's store this morning and started spitting on the new skateboards. Spitting! By the time I got there, Mrs. Kendlemen had sprayed the whole damn place. And she must have had a cold or something. I'm telling you, I won't eat for a week. So, what happened to your crops?
Graham Hess: Morgan, after you were born, the doctor gave you to your mother. When she first looked at you, you just stared right back. You both just stared at each other for longest time, and you didn't even cry.
Merrill: Excluding the possibility that a female Scandinavian Olympian was running around outside our house last night, what else might be a possibility?
Officer Caroline: I'm not done asking questions. And I don't appreciate sarcasm.
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.