You'll never guess where Waldo shows up.

As you may or may not know, a movie "Easter egg" is a joke or reference cleverly hidden in a scene. Pixar's references to its other movies -- a plush Nemo toy in "Monsters, Inc." or the Pizza Planet truck appearing in almost every movie, for example -- are probably the most recognizable examples of an Easter egg, but many other films have at least a few.

Directors have been sneaking (often elaborate) Easter eggs into their movies for years, and though you may have seen your favorite multiple times, you probably missed some of these:

1. R2-D2 has made secret appearances in many movies, including "Raiders of the Lost Ark," along with C-3PO.

The "Star Wars" robots make two appearances in "Raiders of the Lost Ark." First, the pair noticeably shows up as a sort of hieroglyphs on a pillar, right as Indiana Jones finds the ark. Then, shortly after this moment there's an even bigger depiction of the two on a wall behind Jones and Sallah as they lift the ark. This one also features Princess Leia, who is kneeling next to R2-D2 as she presumably uploads data with C-3PO.

Image: "Raiders of the Lost Ark."

2. Frank Abagnale makes a cameo in "Catch Me If You Can," ironically, as an arresting officer of himself.

Leonardo DiCaprio plays Frank Abagnale in "Catch Me If You Can," which was inspired by a true story. In an amusing twist, when DiCaprio's character is finally arrested, the arrest is aided by the real-life Abagnale. Playing a French policeman, Abagnale helps "Abagnale" into a cop car in the small town of Montrichard, France. Speaking to his feelings about the movie, the real-life Abagnale said:

It’s quite flattering to have Leonardo DiCaprio play you in the movie. He’s a great-looking young man ... I was very blessed it was Steven Spielberg who made the movie. He was very much into the redemption side of the story. They asked him in an interview why he had owned the rights to this story for 20 years before he made the movie and he said: "I wanted to see what the real Frank Abagnale did with his life before I immortalized him on film."

Abagnale was close friends with Joe Shea, the FBI agent played by Tom Hanks in the movie, until Shea's death.

Many films based on true stories actually have similar Easter egg cameos, including, "Erin Brockovich," "Apollo 13," "The Pursuit of Happyness" and "Fear and Loathing in Las Vegas."

Image: "Catch Me If You Can."

3. There's a hidden sex scene in the third Harry Potter movie.

In "Harry Potter and the Prisoner of Azkaban," Fred and George Weasley give Potter the Marauder's Map. The map shows all of Hogwarts, including everybody's location on the grounds.

If you wait until the credits of "Prisoner of Azkaban," you can see the map at work, tracking people's movements with footsteps around the halls of Hogwarts. Then, in the bottom left corner, the map reveals four footsteps facing each other in a corner, with two of those footsteps being spread around the others. "Harry Potter and the Prisoner of Azkaban" was rated PG.

4. In "Inglourious Basterds," a leaf falls onto an Austrian-born, Jewish soldier, and its appearance mimics the yellow "Star of David" that Jewish people were forced to wear on the left side of their chest by the Nazis.

Cpl. Wilhelm Wicki left Austria for America when the Nazis began to annex his homeland. Eventually, he joined the Inglourious Basterds and, in a particular moment when translating for a Nazi prisoner, a yellow leaf falls down onto the left side of his chest. Eli Roth, who starred in the film as "The Bear Jew," says Quentin Tarantino did this on purpose:

There’s [a] scene, where a soldier is pointing at a map and a yellow leaf falls on [actor] Gideon Burkhard’s chest. And someone else pointed out that it’s “down to the yellow leaf that mimics the Star of David on that soldier.” And Quentin kept that, and he kept it for a reason.

Image: "Inglourious Basterds."

5. An image of Waldo lying among dead bodies flashes in "Apocalypto."

This only happened in the theatrical release (therefore you have to trust this has not been inserted into the multiple bootleg copies of the original as a hoax), but for some reason Mel Gibson felt it necessary to put a brief frame of Waldo among a sea of dead bodies in the middle of a chase scene. (You can watch it here.)

The movie "Apocalypto" is a gory but serious account of the fall of the Mayan civilization. Waldo is a hilarious addition. Gibson also put a seemingly random image into the trailer of "Apocalypto" -- a shot of his goofily smiling face with cigarette dangling and wild beard.

Image: "Apocalypto."

6. Alfred Hitchcock makes small appearances in almost all of his movies.

Starting in 1927, Alfred Hitchcock made 39 self-referential cameos in his movies, including appearances in "Vertigo," "North by Northwest," "Psycho" and "The Birds." In four of his earlier movies, he made two appearances.

As AMC mentions, the cameos have a few recurring themes. Hitchcock often carried a musical instrument, or acted as a passenger on public transportation, and many were humorous some way, such as the use of his photo for the "before" shot in a newspaper weight reduction advertisement in "Lifeboat."

Hitchcock's appearances usually happen near the beginning of the movie, sometimes even during the opening credits, so you don't need to spend time searching for him rather than paying attention to the plot.

7. After Marty McFly accidentally knocks down a pine tree in the past at the site of the future Twin Pines mall, the name changes to Lone Pine.

Doc Brown and Marty McFly originally meet at Twin Pines mall to travel back in time. When McFly has to go back to 1955, the mall hasn't been built yet and is instead occupied by a ranch owned by a Mr. Peabody. The ranch is named Two Pines, deriving its name from ... two pines.

When McFly has to escape Peabody in his DeLorean (since Peabody believes he's an alien), McFly runs over one of the two pines. The future has been altered and when he returns near the end of the movie to prevent Brown's death, the mall's name has been altered to reflect McFly's accident.

Image: "Back to the Future."

8. David Fincher has said there's a Starbucks coffee cup in "every shot" of "Fight Club."

Although it's more like almost every shot. David Fincher tried to work the Starbucks cup into the movie as much as he could. As he explained:

When I first moved to LA in 1984, you could not get a good cup of coffee in Los Angeles to save your life. I mean, it was really pathetic. Then Starbucks came out, and it was such a great idea: good coffee. And when it became successful there were, like two or three on every block. It's too much of a good thing. But they read the script, they knew what we were doing, and they were kind of ready to poke a little fun at themselves. I mean, they wouldn't let us use their name on the coffee shop that gets destroyed by the piece of tragic corporate art, but they were willing to give us the rest of their stuff. We had a lot of fun using that - there are Starbucks cups everywhere, in every shot ... I don't have anything personal against Starbucks. I think they're trying to do a good thing. They're just too successful.

9. An "X" shows up every time somebody is going to die in "The Departed."

Martin Scorsese put X's all over "The Departed" to foreshadow a characters death. (Here's a roundup of a few of them.) As Cracked notes, the only major character to survive is also the only one to not have any X's -- Sgt. Dignam, played by Mark Wahlberg. Sgt. Dignam actually often appears with straight lines behind him.

This is an homage to the original 1932 version of "Scarface." That movie was even more obvious with its X's, even featuring a huge one in the opening title card.

10. Pac-Man is on a screen for a moment in the original "Tron."

Sark yells at a display screen with Pac-Man's image while searching for Flynn and Tron. Simultaneous with his rising anger, you can hear the iconic "waka waka" coming from Pac-Man.

The movie also has a scene in which the Solar Sailer travels over Mickey Mouse's face. ("Tron" is, of course, a Disney movie.)

Image: "Tron."

11. The "Toy Story" movies are full of homages to "The Shining."

As mentioned, Pixar movies are famous for their Easter eggs, but they are usually self-referential. The "Toy Story" series, however, has many nods to Stanley Kubrick's "The Shining." In the first "Toy Story," for instance, the pattern of the carpet in Sid's house is the same as in the Overlook Hotel. The director of "Toy Story 3," Lee Unkrich, is a huge fan of "The Shining" and even runs his own fan site. Unkrich explained his obsession to Vulture:

I saw it when I was 12, in 1980, for no particular reason other than that it was a new film in theaters. My mom took me to see it. She’d taken me to see a few bad horror films that had affected me really deeply in terms of having chronic nightmares. But still, that didn’t stop her from taking me to see this one. And it turned out to be the best move she ever made -- because it began this 32-year love affair with the film. It was the film that inspired me to become a filmmaker myself.

And if you feel like this ruined the innocence of "Toy Story" for you, give this illustrated "Toy Shining" series a try, which features Woody as Jack Torrance.

Image Left: "The Shining." Image Right: "Toy Story."

BONUS: The term "Easter Egg" may have originated from actual eggs on the set of "The Rocky Horror Picture Show."

The cast apparently had an Easter egg hunt on set and accidentally forgot to find at least three eggs that appear in the movie.

As mentioned above, directors have snuck things into movies for years and years, but this is about actual "Easter eggs." Perhaps just be a legend, but apparently the cast of "The Rocky Horror Picture Show" had some fun on set with their own Easter egg hunt and then ended up missing a few of the eggs. These made it into the movie and supposedly became the origin of the movie term.

As the fan site Cosmo's Factory points out, three random eggs can be seen in the movie: "under Frank's throne, one instead of a light in the main room, one as the group goes up in the elevator to the lab."