In Looper (2012), Joe starts explaining time travel to Sara, and she says "You're a looper?" How did she know what a Looper was? What was her previous tie to the criminal world?
I read a fascinating review/article that mentioned in passing this plot point. The author of this review put forward a theory which blew my mind.
We see in the movie that not just "Loopers" and people sent to disappear are sent to the past. We saw that Abe was sent back from the future to hire Loopers and keep an eye on that end of things.
In the end Sara convinces Cid that she is his mother and it was her "sister" who was killed accidentally by his tantrum. What if Sara was sent from the future to the year 2044 so that Cid would have a stable childhood and not grow to become the Rainmaker?
Here is a quote from the article (which the writer/director Rian Johnson retweeted so probably thinks is an interesting theory if not what he was planning when writing it):
Sara sits down outside of her house, and pantomimes taking a drag from a cigarette, while spinning her free hand. She does the exact same thing later, just after sleeping with young Joe. She’s smoking while using her TK powers to float her lighter. THIS event is the final thing that ensures that Joe cares enough about the two of them to kill himself to prevent old Joe from turning Cid into the Rainman. It should also be noted that Cid - who is a GENIUS - also says candidly that she’s not his mom.
This means she’s could actually someone looping back to care for Cid, after he accidentally killed his real mother in a psychic tantrum. This would explain how Cid originally came to be motherless and turn into Rainman without old Joe’s involvement. This would also explain how she knows about Loopers, why she does’t shoot Joe when she sees him, why she bears a striking resemblance to Joe’s hookup Suzie so as to attract him, and how she would know what to do in order to ensure that Cid doesn’t become Rainman.
…or maybe that’s all just a clever coincidence. ;)
From TV Tropes:
How does Sara know about loopers?
They're known about in various circles, and may just be kind of that thing you don't discuss, like the mob in general. She may have just heard about it in passing, which could be part of the reason why she chose to move so far away from city life.
Its implied that she was a hooker, and that she probably had Loopers as clients.
This is tangentially addressed in an earlier version of the film's script. In short, 'loopers' aren't nearly as secret as Joe thinks they are. Sarah has heard 'stories' about them from her prior contacts.
[Joe breathes hard, bleeding in the dirt with a shotgun in his nose. But he forces calm. A beat. Then he starts talking.]
JOE: Time travel hasn’t been invented yet. But in thirty years it will be.
[Sara sits. Joe weakly talks, the end of a long explanation.]
JOE: I can’t go back to the city and find him cause Abe, the boss, all his men are going to search the streets 24/7 till they turn up me or... him. All I have is this map. And that he’s coming here.
[Sara stands. Paces away. Deep in thought.]
SARA: A Looper.
JOE: Yeah. Did you know about Loopers, what we do
SARA I’ve heard stories. So he’s coming here to murder me and my son because he thinks we might be this Rainmaker...
Sara used to hang with a bad crowd in 'the city'. What she did (prostitution, presumably) remains unspoken, but we can assume that it involved being around the sort of criminals and ne'er-do-wells that might talk about 'loopers' in hushed tones.
SARA: (sharp) He’s my son. (beat) I had Cid when I was twenty two. But I didn’t want to give up my life. In the city.
[The word “city” has weight for her. Implies volumes.]
From a mere writing standpoint it could just have been a shortcut, so that Joe doesn't get a hard time explaining to her all the things she surely wouldn't believe, which wouldn't bring the story much further (Ok, maybe it could have opened other interresting conflicts and sub-stories, but well).
And in fact when he started "time travel is not possible, but in thirty years..." I found myself thinking nerved "Whoa man, stop it, she's never gonna buy that" only to be relieved when she said "You're a looper", thinking "thanks, not a hard long mistrustful explanation session".
I'm not saying that's the only reason (or that everybody would have felt like me and explaining it to her couldn't have been a good story arc, too) and there is no in-story explanation. But seeing that not everything in Looper was that thought out well, it's a possibility.