There's no denying that even the most modest Hollywood production tends to require the services of literally hundreds of on-set personnel.
As a result, and in an age where everyone has a high-quality camera in their pocket, it's becoming increasingly tricky for filmmakers and studios to keep the lid on their top-secret projects.
After all, Avengers: Endgame's time travel twist was known months before Avengers: Infinity War even came out due to some sneaky leaked set photos, and as long as fans are aware that a movie is in production, they're always going to be on the lookout for a scoop.
But what if they don't even know the movie is being shot?
That's the ingenious tactic pulled by these 10 films, all of which were shot in complete secrecy, with their existence only being confirmed once principal photography had been completed.
Hell, in a few cases audiences weren't made aware of the movie until post-production was basically done and it was just a month or two away from release, serving as a testament to the cast and crew's commitment to keeping schtum.
In an era where huge movies are endlessly hyped for potentially years before finally coming out, it sure is refreshing that these films came together before anyone even knew about them...
10. 10 Cloverfield Lane
In a virtually unprecedented move at the time, Cloverfield spin-off 10 Cloverfield Lane was announced less than two months before it hit cinemas, by which point it was already deep in the final stages of post-production.
Always one to love a mystery, producer J.J. Abrams had the movie shot under the unassuming title "Valencia," and it was only during production that he committed to giving the low-budget sci-fi monster movie an immediate tie to Cloverfield.
This was covert enough that even two of the movie's stars, Mary Elizabeth Winstead and John Gallagher, weren't aware of exactly how intimate the link between the two films would ultimately be, and Abrams only came up with the final title shortly before the first trailer dropped.
As much as Abrams' love of the "mystery box" can frustrate, this was an undeniably genius feat of covert filmmaking and "gotcha!" movie marketing.