Even if you consider yourself a movie buff, we all miss some things the first time we watch our favorite films.
Whether it's a visual joke that's only on-screen for a few moments, or a tiny detail you wouldn't notice unless you watched the movie over and over, filmmakers love to hide little Easter Eggs in their work.
Test yourself by reading this list of 13 of our favorite hidden jokes, details and references and see how many you already knew.
1. Jurassic Park gives its plot away
Jurassic Park isn't famous for its complicated plot, it's just a fun movie about dinosaurs trashing a theme park, but there is a twist partway through when the scientists discover the park's female dinosaurs can mate.
But if you're paying attention this is revealed at the start of the movie: during the helicopter ride to the park, Sam Neil's seat belt has two "female" connectors, but he makes it work by tying them together. "Life finds a way!"
2. There's a joke hiding in the credits for Frozen
We're sorry for reminding you about Disney's smash hit animated musical, because the songs are bound to be stuck in your head all day now.
But even if you know every word to "Let It Go" you probably never noticed the secret in this movie's credits: a clever joke about Kristof and his claim that all men eat their boogers. Blech!
3. Fun with time travel in Back to the Future
Another "blink and you'll miss it" joke, this one is hiding in the classic 80s comedy Back to the Future. At the start of the movie, Marty meets the Professor at the Twin Pines Mall.
But after running over a tree in the 1950s, Marty returns to the present for the film's finale at the Lone Pine Mall. Get it?
Click the next page for more movie secrets, including Star Wars and Harry Potter!