1.In Hereditary, during a scene that cuts from day to night, you can see the house surrounded by coven members in the dark.
2.During a party scene in Hereditary, some kids can be seen watching a film that's depicting someone being beheaded — a common theme throughout the movie.
3.In The Descent, before the monsters are introduced into the story, you can spot one of them peeking out in the cave before vanishing a moment later.
4.In Saw, John Kramer is seen in the hospital with a notepad in front of him that has a drawing of the reverse bear trap mechanism.
5.A shot in The Conjuring 2 resembles a photo taken inside of the Amityville house, showing a child with glowing eyes eerily peeking out of the door.
6.The name of the demon nun, Valak, is visible throughout the The Conjuring 2. For example here, the letter decorations on a shelf spell Valak.
7.In It, when Pennywise wants to lure Georgie into the drain, he changes his eye color from yellow to blue, the same as his brother Bill's. This is something that's specifically mentioned in the novel.
8.Later on in It, when Pennywise shows his Deadlights, you can hear a boy's soul screaming for help.
9.Screamwas directed by Wes Craven, who briefly appears in the film as a janitor dressed like Freddy Krueger, another character he created.
10.In 28 Days Later the infected don't typically speak, but one boy can be heard saying, "I hate you" before Jim kills him.
11.In The Cabin in the Woods, amongst the many monsters in the elevator scene, you can spot two zombies from the Left 4 Dead video game franchise.
12.In The Shining, Jack can be seen wearing a shirt that says "Stovington" — the name of the school Jack taught at in the novel.
13.In Signs, the alien caught on camera is purposely posed like the famous Bigfoot picture.
14.In Halloween H20, Janet Leigh plays Norma. Leigh also played Marion in Psycho. In one Halloween H20 scene, a slowed down version of the classic Psycho music plays as Norma walks to her car, which is the same car she drove in Psycho.
15.In Donnie Darko, a pumpkin carving seen in the kitchen looks like Frank's bunny mask.
16.In Get Out, Rose hangs up the photos of her ex-boyfriends that Chris discovered earlier.
17.In A Quiet Place, the aisles in the pharmacy are empty except for the chips section, because they make too much noise.
18.In I Am Legend, a poster for a Batman vs. Superman movie can be seen — a prediction that came true nine years later in 2016's Batman v Superman: Dawn of Justice.
19.In Final Destination, after he's nearly killed by a train, Carter can be spotted having peed his pants.
20.In Final Destination 5, a sign shows the bridge with a part of it scratched out, foreshadowing its collapse later on.
21.In Insidious, a drawing of Billy the Puppet from the Saw movies can be seen on a chalkboard.
22.In Insidious: Chapter 2, the VCR label has letters scratched out, so instead of Panasonic it reads, "Panic."
