Sometimes films purposefully leave unresolved questions to keep audiences thinking and talking about it long after they've finished watching.
Why wouldn't Rose let Jack climb aboard the piece of wood? Why do the Terminators have to travel back naked? and How many more Transformers movies will Michael Bay churn out?
Those questions aren't answered, but these highly-debated questions have been...
10. How did Marty and Doc Brown become friends?
In Back to the Future, skateboarding, guitar-playing high school student Marty McFly is friends with older oddball inventor Doc Brown, how did this come about? Should the authorities be alerted over this over this quiestionable duo?
One of those questions was answered by BTTF co-creator Bob Gale, who explained that they thought about the pairing while they were coming up with the characters.
Gale explained: "We never explained it in the movie. But the history of the characters that Bob Zemeckis and I created is that for years, Marty was told that Doc Brown was dangerous, a crackpot, a lunatic.
"So, being a red-blooded American teenage boy, age 13 or 14, he decided to find out just why this guy was so dangerous. Marty snuck into Doc’s lab, and was fascinated by all the cool stuff that was there.
"When Doc found him there, he was delighted to find that Marty thought he was cool and accepted him for what he was.
"Both of them were the black sheep in their respective environments. Doc gave Marty a part-time job to help with experiments, tend to the lab, tend to the dog, etc.
"And that’s the origin of their relationship."
So, that's how it all began, and we got to enjoy their slightly unusual, time-travelling, bully-beating, almost-incestuous friendship.
9. Was Deckard a replicant?
Many involved with Blade Runner are sure that Deckard was a human, including Harrison Ford, executive producer Hampton Fancher, screenplay writer David Peoples and even Philip K. Dick who wrote the original novel.
Meanwhile, director Ridley Scott is certain that Deckard is a replicant.
In one shot, an out-of-focus Deckard's eyes briefly luminesce and Scott included a scene of Deckard dreaming of a unicorn after Gaff left the origami unicorn - this suggests that Gaff knows about Deckard's dream in the same way that Deckard knows about Rachel's implanted memories.
The studio wasn't so keen on Scott's take on Deckard, so cut the dream sequence and another few moments which would have backed up the replicant arguement.
As the director's cut restored these scenes, it's up to you whether you want to side with Ridley Scott or Harison Ford.
8. Did Pan's Labryrinth happen in Ofelia's head?
The Guillermo del Toro dark fairytale set in General Franco's Spain about a bookish young girl introduced us to that weird eye-hand creature, gigantic frog and goat-like Faun.
The tale of Ofelia finding out she is a princess and surviving the gruesome tasks to prove her royal lineage is a fantastical and terrifying, but was it real or did it happen all in her head?
While it's never revealed during the film, director Guilhermo del Toror stated: "I think it's real, but it's real not in the pejorative sense.
It's a spiritiual reality. I don't mean the faun is there, or the mandrake is there, but she really is transported - saved by herself."
So there you go, it's real, but like, sort of not.
7. What does Bill Murray whisper to Scarlett Johansson?
When faded film star Bob Harris - played with deadpan excellence by Bill Murray - and Scarlett Johansson's negelected young woman Charlotte say their goodbyes in a crowded Tokyo street, their touching moment is punctuated with Bob whispering into her ear.
Forget all the mysterious subtelty of the scene, people want to know what he said, it was probably something hilarious - it is Bill Murray after all.
According to the script, a line was never in there, only a cue for Murray to ad-lib the line, which doesn't help matters any.
The script does indicate though, what is going through Bob's head - that he wants to tell Charlotte that he loves her, but chickens out at the last minute.
People with plenty of time, software and enthusiasm on their side have attempted to decode the whiper with audio-processing software, and here is what it might be:
Yeah, this question hasn't been really answered conclusively, but we're on the right tracks, so that's the main thing... right?
6. What's in the Cast Away FedEx box?
When Tom Hanks' character Chuck Noland is marooned on a desert island in the Pacific with only a volleyball for company, he leaves one of the FedEx packages that wash ashore unopened.
When he is rescued, Chuck travels to Texas to return the still-unopened present to a woman named Bettina, only to find the house is empty and leaves it without us finding out what was in the mysterious present.
In a draft of the script, on his 1,000th day on the island, Chuck whips open the angel wing FedEx box, to discover that it contains two bottles of salsa verde. Yep.
The package is sent from Bettina to her husband, the naked cowboy at the beginning of the film, with a note that she wants to spice up their relationship... just like salsa.
The draft ends the film with Chuck delivering the package to Bettina and letting her know that he was glad that her husband never got the salsa, because he was a jerk.
4. What was on the secret disc in Neo's apartment
Early on in The Matrix, a group of people turn up to Neo's apartment, where he hands them a disc in exchange for $2,000, when he notices that one of the girls has a white rabbit tattoo which takes him on a series of wacky adventures.
The disc is never mentioned again in the film, but what was so important that some industrial techno clubbing chap would pay two grand for it?
Parking tickets. In an earlier draft of the script, 'Anthony' turns up at Neo's door so he can wipe all of the outstanding parking tickets - so he must have had more than $2,000 worth of them.
This irresponsible parking was written out in order to make way for heavy-heanded foreshadowing, leaving it a more interesting mystery instead.
3. What caused the Groundhog Day time loop?
The much-loved '80s comedy in which Bill Murray is forced to repeat the same day again and again in the wintery town of Punxsutawney, Pennsylvania.
What is never explained in the endlessly repeating days was what caused weatherman Phil Connors into infintely reliving 2nd February.
In the second draft of the script, it is Phil's recently-dumped girlfriend who puts a curse on the weatherman.
While Phil is going to bed in Punxsutawney, the scene is intercut with his ex-girlfriend Stephanie using Phil's business card and broken watch (frozen at 5:59) to perform a magic spell from a book titled 101 Curses, Spells and Enchantments You Can Do at Home.
With subsequent mystery-solving, the screenplay specifies that Phil spends 10,000 years trapped in the loop and that the reason he comes out is that the kiss with Rita breaks the spell.
Keen-eared viewers can hear a 'tingle' sound when they Phil and Rita kiss, even though the curse isn't alluded to at all in the finished film.
2. Are Arnie's Total Recall memories implanted or real?
Arnie's mind-bending sci-fi classic in which he visits a company that implants memories only for things to get out-of-hand, as Arnie struggles to believe what is real and what is hallucination.
The film never states whether it is all Douglas Quaid's memories or if he is secret agent Carl Hauser who has had his memory erased.
That is, until you watch the director's commentary in which Paul Verhoeven explains that, at the end of the movie when the screen fades to white instead of black, it is the indication that it's all an hallucination.
Verhoeven added that despite his interpretation, Arnie played the part that he was Hauser and that it was all real - which helped to add to the film's unclear resolution.
1. What is in the Pulp Fiction briefcase?
The glowing contents of the highly-sought after briefcase belonging to Marsellus Wallace has long been debated by Tarantino fans over what exactly they are.
Theories popularly shared online include Marsullus Wallace's soul (which had been removed through the back of his neck) or the gold Elvis suit worn by Val Kilmer in True Romance.
Well prepare to be disappointed because the contents are diamons, boring old precious stones.
Roger Avary, who co-wrote Reservoir Dogs and Pulp Fiction with Tarantino, confirmed that the script originally said that the case was full of diamonds.
As the main event in Reservoir Dogs was a diamond heist, Tarantino didn't want to include it in his second films, also it's a kind of obvious and boring answer.
Someone working on the film had the 'bright' idea of sticking an orange lightbulb in the case to give it that mysterious and much-debated glow.
Avary wasn't so keen on the glow, he explained: "Suddenly what could have been anything became anything supernatural; they didn't need to push the effect.
"People would have debated it for years."
Indeed they have.