Some lines are so good one would assume that the writers spent years meticulously trying out an infinite combination of words until the sentence was perfect. That's why it's shocking that some of the most memorable lines in science fiction history were made up on the spot. Here are some of those most quotable of quotes.

Blade Runner

The line: "All those... moments... will be lost in time, like [small cough] tears... in... rain. Time... to die..."

The last line of Roy Batty's final monologue was improvised by legend Rutger Hauer. Originally the speech was supposed to be two pages. He cut it down to both save the audience from having to sit through another long death scene, but also to get out of the rain.

They Live!

The line: "I have come here to chew bubblegum and kick ass... and I'm all out of bubblegum."

When asked Rowdy Roddy Piper had this to say about his ad lib:

Yeah. I couldn't tell you what it really means either. It was one of those – "Roddy, you've got bullets on you, you've got a shotgun, you've got sunglasses, you go into a bank, you're not gonna rob it, say something … action!" I'm all out of bubblegum. Lunch! That was it. No more than that. I know, it's crazy.

Aliens

The line: "That's it, man. Game over, man! Game over!"

Paxton comments:

That was an ad-lib thing, too. [Laughs.] Now, when I say "ad-lib," I'm not clever enough to think of stuff and throw it out off the top of my head. It's usually something I'll come up with beforehand, and then I'll try it out. I find most directors are willing to let you kind of bend the dialogue if you give them something different.

Jaws

The line: You're going to need a bigger boat.

This is possibly one of the most famous lines in cinema history. The way it works with the pacing and soundtrack is absolutely brilliant. Famously ad-libbed by Roy Scheider, it proves that some of greatest movie moments just can't be written ahead of time.

The Warriors

The line: "Warriors...come out to plaaaaay!"

David Patrick Kelly recalled:

I wanted to make Luther evil, so he was influenced by this really bad guy who I knew in downtown New York who would make fun of me and say, "Daaaaave. Daaaaave. Daaaaave." And it was the creepiest thing I ever heard.

Star Wars: the Empire Strikes Back

The Line: Leia: I love you! Han: "I know"

This line was actually a pretty big point of contention between Ford and George Lucas as Ford tells it:

It was such a contest between George and I about whether that was appropriate or whether the audience would enjoy that line or not, to the point where he made me go to a test screening to sit next to him to prove it was going to get a bad laugh," Ford recalled with a smile. "And it didn't. It got a good laugh. So it stayed in.

A Clockwork Orange (NSFW)

The Line: Alex sings Singing in the Rain during a violent rape scene.

Kubrick had this to say about the controversial scene:

I was also rather pleased with the idea of 'Singin' in the Rain' as a means of Alexander identifying Alex again towards the end of the film.

This was one of the more important ideas which arose during rehearsal. This scene, in fact, was rehearsed longer than any other scene in the film and appeared to be going nowhere. We spent three days trying to work out just what was going to happen and somehow it all seemed a bit inadequate. Then suddenly the idea popped into my head — I don't know where it came from or what triggered it off.

Armageddon

The Line: "The United States government just asked us to save the world... anyone want to say 'no?'"

This line, according to tvtrope.org, was improvised by Bruce Willis. Evidently Michael Bay was a fan of the ad lib, as he put it in the trailer.

District 9

The lines: Most of Wikus' dialogue while evicting the prawns.

In an interview with io9 the director had this to say about these scenes:

So we would film the two of them and then we would go to a different shack. And he'd pretend to evict a new alien. Then we'd go somewhere else and somewhere else. So it was just the two of them. It's the conversations between those two, the actual dialogue and what actually came out of them was totally improved. Any details in words and the language between the two happened right there on the day of shooting. That what makes it feel like they are really communicating...

But stuff like when he walks up in to the shack and says, "this is a gang sign, we're in a gang area right here," we would draw the sign on the wall and he would randomly say it's a gang area. And that meant because he's walking up to a shack that has an alien in it with a whole story that we've written with those guys distilling their fluid and I'm like, "that's interesting you just said that the supporting alien character is a gangster." But if it works, we keep going.

Shaun of the Dead

The lines: Ed's description of the other patrons at the Winchester is all improvised.

At a panel in Australia Nick Frost and Edgar Wright discussed this scene:

EW: The vogue at the moment in comedy is to improvise a lot, but usually what that comes down to is people arguing and, in most improv comedies, the improvvie bits are people arguing with each other. It's never usually, like, plot-related because the plot has to move the story along, and improv rarely does. I think the only bit in this film that was really improvised was when you were trying to make Simon laugh.

NF: "Cafe au lait", all that kind of stuff. "Cockocidal maniac", I think was improvised. Because that was your mother-in-law behind, wasn't it?

Indiana Jones and the Last Crusade

The line: She talks in her sleep. (Line at 21.08)

Julian Glover, the man who played Walter Donovon, was on set the day Sean Connery came up with one of the funniest lines from the movie:

My favourite memory is Sean making up that line, "She talks in her sleep." It was on the spot. Harrison said, "How did you know she's a Nazi?" and he said that, and they had to stop filming. Everybody just fell on the floor and Steven said, "Well, that's in."

A Nightmare on Elm Street 3: Dream Warriors

The line: Welcome to prime time, bitch!

Apparently out of any one liner Freddy has said in the Freddy movies, according to his Reddit AMA, this is his favorite.

My favorite is my improv from part 3, "Welcome to Prime Time Bitch."

Englund also talks about how he goes about improvising in the interview with MTV News:

Englund says he doesn't have any input on the "Nightmare" movies until he signs on to act in them. Even then, his input is not as major as you would think — though he cites the famous Freddy line "Welcome to prime time, bitch!" as his brainchild. He mostly lets the director and writer handle the duties of the script.

Serenity

The line: Faster! Faster would be better!

From the Serenity DVD commentary:

Joss Whedon: That last line, by the way, "Faster would be better"… This is one of the reasons I love working with Nathan so much. I went up to him and said, "Say something Mal would say." I just felt we needed a little line there and I was in a hurry and I hadn't written one and so he just improvved "Faster would be better", which was such a good Mal line that I was like, "Why did I slave away at that script for so many months? Why don't you just say stuff?" He's extraordinary that way. He can really become the character.

Star Trek 2009

The Line: All I've got left are my bones.

According to the audio commentary for the movie, J.J. Abrams has commented that the "bones" line was not originally in the script, but improvised by Karl Urban, a long time Star Trek fan.

Bonus: The fantastic line by Simon Pegg as Scotty,"Can I get a towel?" Was also an ad lib. Here is a pretty great video of Zachary Quinto describing the scene: