Video report by ITV News Correspondent Ben Chapman
Knives Out film director has unveiled a secret in the world of product placement - villains cannot use an iPhone on the big screen.
Johnson, whose film credits include Star Wars: The Last Jedi and Looper told Vanity Fair "bad guys cannot have iPhones on camera".
He pointed out the Apple caveat while dissecting a tense scene between all of the Thrombey family members ahead of the reading of the late Harlan Thrombey’s will.
A mobile phone then becomes a spoiler as during the scene, Jamie Lee Curtis' character Linda Drysdale can be seen with an iPhone, prompting Johnson to reveal the behind-the-scenes secret.
He let the secret slip in a video, saying: "Apple, they let you use iPhones in movies, but – and this is very pivotal – if you’re ever watching a mystery movie, bad guys cannot have iPhones on camera."
He revealed the clue to whodunnit on films as he discussed Knives Out, a murder mystery film with an ensemble cast featuring Daniel Craig, Toni Collette and Jamie Lee Curtis.
Johnson added: "So oh no, every single filmmaker that has a bad guy in their movie that's supposed to be a secret wants to murder me right now."
So how common is this? Fairly so, says product placement specialist Darryl Collis.
"With feature films, every production needs the brand's permission to show a brand within the film," he told ITV News.
"So if Apple don't give clearance for that to appear, then what will have to happen is they'll either have to remove the logo or that brand can't appear in the film.
"A good example would be Coca Cola were featured in a film called Slumdog Millionaire, but they were shown in a negative light so what they said to the producers is: 'You cannot show our brand, you need to remove the labels.'
"They never gave clearance for the brand to appear so they had to remove the labels at the end of the post production."
But will it spoil movies for film buffs?
Film critic Hannah Woodhead works at Little White Lies magazine, she told ITV News she'll be much more eagle-eyed now one of the secrets of Hollywood is out of the bag.
"I think for most people they'd be able to suspend disbelief and kind of forget the whole if you have an iPhone you're not going to be the bad guy long enough to enjoy the movie.
"But for someone like me who watches a lot of films and is very tapped in, I now can't unhear this."
Knives Out amassed more than £250 million at the global box office since its November release, a sizeable return on a £35 million budget.
The film became available on 4K, Blu-Ray and DVD on Tuesday and Johnson is currently working on a sequel to the film.