Like any good whodunit, Knives Out (2019) is filled with twists that keep viewers guessing who the true villain is throughout the film. But there's a major clue as to who the good guys and bad guys are hidden in plain sight. To spot it, just look at what type of smartphone the characters are holding.

As Knives Out writer and director Rian Johnson revealed in a recent video for Vanity Fair, Apple won't let an iPhone appear on film if it belongs to a villain. "I don't know if I should say this or not," Johnson said. "Apple, they let you use iPhones in movies[...]but bad guys cannot have iPhones on camera[...]Every single filmmaker who has a bad guy in their movie that's supposed to be a secret wants to murder me right now." You can listen to the tidbit at the 2:50-minute mark in the video below.

Apple has long used product placement in movies and television shows to promote its brand. There's even reportedly an employee at Apple whose job it is to work with Hollywood to get MacBooks and iPhones into the hands of characters on screen. The ubiquity of Apple gadgets in media means the lack of one could be a legitimate spoiler in a murder mystery. Apple has also been tight-lipped about its product placement rules, making Johnson's revelation an especially juicy insight.

If you're looking for more film secrets, check out these hidden messages in the backgrounds of your favorite movies and TV shows.

[h/t The Next Web]