For some fans, it isn't enough to merely watch a movie.
No, some obsess over the tiny details of a film, spotting things that others would barely notice.
Finding Nemo is the latest movie to be subjected to intense fan-study. One Twitter user recently noticed something in the opening scene of the 2003 animated movie.
It shows an image of Nemo's fish egg with a hairline crack in the shell. This, could explain the origins of Nemo's tiny "lucky fin".
It's a cute little detail that probably bypassed most viewers.
There's no shortage of similar fan theories about movies, put forward by people who claim to have worked out the real meaning behind a story or its characters (no matter how unlikely or bizarre it might seem).
With that in mind, here are seven other movie classics that have inspired some of the most thought-provoking, brilliant and just plain bonkers fan theories ever.
Harry Potter (2001-2011):
Naturally, Potter has produced a whole realm of fan theories, at least one of which has been endorsed by J.K. Rowling herself.
One of the most haunting Potter theories is that everything in the series took place in Harry's imagination; that he lost his mind while living in the cupboard under the stairs at the Dursley's, and conjured up the whole Hogwarts adventure as a coping mechanism.
Jurassic World (2015):
One theory has it that Chris Pratt's character, Owen Grady, is the grown-up version of a child character from the original 1993 Jurassic Park movie - namely the young kid at the start of the movie who gets a memorably graphic lecture on raptors' killing strategies from Dr Alan Grant (Sam Neill).
The logic is that the kid character would roughly be the same age in 2015 as Pratt's in Jurassic World, and that Alan Grant had made such an impression on him that he devoted his life to treating raptors with love and respect.
For the record, the actor who played that young kid, Whit Hertford, thinks the theory is bogus.
Home Alone (1990):
What if the burglars, Harry and Marv (Joe Pesci and Daniel Stern), are not the real villains of the 1990 Christmas classic, after all? And the real bad guy orchestrating the crime is actually Kevin's Uncle Frank?
That's what one theorist believes. The explanation goes that cheapskate Frank plotted everything from Kevin (Macaulay Culkin) getting sent to the attic and missing the ride to the airport, to cutting the electricity and knocking out the alarm clocks, to arranging for the bumbling burglars to murder Kevin!
Why would he do this, you may wonder? Primarily to cash in on his brother's wealth by having him robbed. But when Frank learns that Kevin has been left at home, the theory goes - and a quick screen grab apparently hints- that Frank called Harry and Marv and instructed them to do away with Kevin because he knew too much.
This is really out there. One theory put forward by writer Mary Katharine Ham claims that the 2010 Disney kiddies' animation is inspired by the horror classic The Shining.
The evidence is compelling. For example, take the comparison between Frozen's Elsa, and The Shining's Jack Torrence. Both films have "a menacing main character who is a danger to family members, whose volatility increases after a long isolation inside a giant, ornate, high-ceilinged building in a cold, desolate landscape."
Meanwhile, Elsa's sister Anna is compared to little Danny in The Shining ("the innocent protagonist touched by the supernatural"), while snowman Olaf is seen as a newer version of the wife Wendy (Shelley Duvall) from the earlier horror movie (the "goofy supporting character...who will sacrifice anything to protect our innocent protagonist from danger").
Toy Story (1995-2010):
Even having one of the trilogy's writers rubbishing that theory hasn't killed off speculation.
Then there's a hypothesis that Sid, the demonic kid from the first movie, appears as a grown up bin man in the third instalment.
Another theory which won't go to bed is that Andy's mum was the original owner of Jessie the cowgirl, first introduced in Toy Story 2. That would make Andy's mum 'Emily', about whom Jessie sings the heartbreaking ballad 'When She Loved Me'.
Even Tom Hanks, who voices Woody, is a fan of that one.
Here's a doozy for you: Leonardo DiCaprio's character, Jack, is a time traveller sent back to 1912 to prevent Kate Winslet's Rose from taking her own life.
The theory goes that if Rose had died or gone missing, the ship would have stopped and never hit the iceberg, changing history forever.
One of the most persistent fan theories is that Bond is a Time Lord, which is why he has been played by multiple actors over the decades.
The most recent Bond theory has it that Bond experienced brain damage during the head-drilling sequence in Spectre (2015) - and, as a result, Daniel Craig's Bond hallucinated every other Bond adventure starring other actors in the role.
If that were true, it would be one of the biggest childhood-memory-scarring revelations since...well, yesterday, when we learned that Mario is no longer a plumber.
We need a lie down after all that.
Want some more?