And even if you were able to keep your eyes open the entire time, there are a number of callbacks to the original stories and other Easter eggs gather throughout out the movie.

Here's everything you might've missed.

And warning: spoilers ahead.

While the books were written in the early 1980s, the film is set in 1968.

Producer Guillermo del Toro has said that this date was chosen because he considers it an end of innocence for America.

And that the Vietnam War is a sort of ghost that looms over the town, with kids literally going missing as they head off to war.

There are a number of references to this time period and the war in the movie.

The school is putting on the 1960s musical "Bye Bye Birdie," which was based on Elvis Presley being drafted into the Army.

In the movie, the character Ramon is a draft dodger.

On a school bulletin board, you can see the lyrics to the Pete Seeger song "Turn! Turn! Turn!" which was covered by The Byrds in 1965 and became popular as an anti-war anthem.

The drive-in theater is showing "Night of the Living Dead."

This classic black-and-white horror film was first released on October 1, 1968.

Del Toro has described George Romero as an iconoclast.

The book featured in the movie was actually inspired by a book from another del Toro movie, "Pan's Labyrinth."

In that film, the main character, Ofelia, is given "The Book of Crossroads," which also writes itself.

If you listen carefully, the music actually changes slightly each time a different story is being featured on the screen.

According to composer Anna Drubich, "Harold" centers around guitar and banjo.

"The Big Toe" is mostly brass.

"The Red Spot" involves string instruments.

"The Pale Lady" has woodwinds.

And "The Jangly Man" is heavy on percussion.

Some of the characters in the film are directly from the original books, and others are new.

The character who is chased by Harold is named Tommy.

In the books, he's named Thomas.

But instead of transforming into a scarecrow, the character in the books is skinned by the monster.

Ruth is both the name of the girl in "The Red Spot" and the victim of the spiders in the movie.

The boy in "The Big Toe" has no name, and neither do the characters featured in "The Haunted House" or "Me Tie Dough-ty Walker."

The monsters were all created to closely resemble the creepy drawings by the book's illustrator, Stephen Gammell.

So the filmmakers stuck to the black-and-white theme as much as possible and desaturated the colors on the creatures.

And each monster is played by a famous creature performer that you have likely seen before.

The actor who plays the Jangly Man is Troy James, a contortionist who has appeared on "America's Got Talent."

Yes, he was actually walking in that twisted, upside-down manner in the movie.

The actor who plays the toeless corpse is Javier Botet.

He has Marfan syndrome, a genetic disorder which makes his body longer and thinner.

Botet has also played various creatures in other films, including "Slenderman," Melisandre's true form in season eight of "Game of Thrones," "Mama" in the del Toro horror film, and the creepy sick hobo in "It."

Harold and the Pale Lady were both played by Mark Steger.

Steger was the man inside the demogorgon costume in "Stranger Things."

Sarah Bellows appears to be loosely based on a character in the first book of the series, from a story called "The Haunted House," in which a preacher encounters a dead woman who emerges from the basement and wants revenge for her murder.

But the drawing associated with this story was actually used as the face of the toeless corpse in the movie.

While most of the monsters in the movie are straight from the specific stories in the books, the Jangly Man is actually a new character inspired by multiple creatures.

In particular, he was taken from the story "Me Tie Dough-ty Walker," in which a severed head falls down a chimney.

In the original story, a dog responds to the severed head's strange chant with one of its own.

"Lynchy kinchy colly molly dingo dingo," and it drops dead when the head appears.

But in the film, it just sort of growls and runs away.

Auggie dresses up for Halloween as a clown, but not just any clown.

The black-and-white suit is the signature look of the 17th-century clown Pierrot, featured in performances known as commedia dell'arte.

When he's being chased through the house by the toeless corpse, you can see a poster on his bedroom door featuring another standard character from the genre, Arlecchino.

The song that plays on Sarah Bellows and Lou Lou's music box might sound familiar.

It's called "The Hearse Song," which is famously featured in the first book.

It's based on a real song about death sung by American and British soldiers during World War I.

At one point, the kids visit Pennhurst Hospital, the scene of Chuck's Pale Lady encounter.

Pennhurst was a real asylum in Spring City, Pennsylvania, that closed in 1987 and has now been reopened as a haunted attraction.

When Stella is flipping through Sarah's book, we see several other stories from the original books that weren't featured in the movie.

These include "The Wendigo," about a man who mysteriously disappears in the woods.

"Strangers," about a man who meets a ghost on a train,

"The Cat's Paw," involving a woman who turns into a cat and loses her foot.

And "The Attic," in which a man is trying to find his missing dog in his own attic, opens the door, and screams because he steps on a nail.

In the beginning of the movie, we see a short horror story in Stella's bedroom that's not in the "Scary Stories" books called "The Whistling Room" by William Hope Hodgson.

And her bedroom is also full of shout-outs to some obscure horror films from the 1950s.

There are posters from movies like "Beast from Haunted Cave," "Mesa of Lost Women," "Frankenstein's Daughter," and "Indestructible Man."

Did we miss anything?

Let us know in the comments.