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After you've unwrapped the presents, enjoyed your holiday brunch, watched It's A Wonderful Life and gotten your fill of A Christmas Story, there's one holiday classic left to screen on Christmas Day—National Lampoon's Christmas Vacation.

Audiences were introduced to the loving if dysfunctional and slightly inept Griswold family in the raunchy, laugh-out-loud comedies Vacation and European Vacation. In this film, which was released on December 1, 1989, audiences followed the Griswold family home where they were preparing for the holidays with visions of sugar plums and impressive light displays dancing through their heads. As in the other film's in the franchise, the Griswolds plans were derailed by their own cluelessness and clumsiness—and Cousin Eddie, of course. One great thing about the film is that it shows that you can have a merry, memorable Christmas even if you can't quite pull off that Norman Rockwell thing.

Here are 12 festive facts you may not know about this Christmas comedy classic:

1. Christmas Vacation is based on a short story.

John Hughes, the legendary ‘80s filmmaker, wrote a nostalgic short story in National Lampoon magazine called Christmas '59, all about a family "to have one of those fun old-fashioned Christmases that people on TV have". (You can read the story here.) The film includes several iconic scenes that Hughes included in the story, including the Griswolds struggle to find the perfect Christmas tree, the disastrous turkey dinner, and Aunt Bethany wrapping up her cat (although it was a dog in Hughes's story).

2. The director had never seen a Vacation film before

Jeremiah Chechik, was brought in to direct the film, even though there were a few glaring warning signs on his resume. First, he is Canadian and hired to make a movie about a very American holiday. Second, he reportedly hadn't seen any of the other films in the Vacation franchise. Luckily, Chechik was able to over come those obstacles and made a comedy classic anyway.

3. There were only two Christmas movies released in 1989 and they starred the same actor

Johnny Galecki, better known now for his role in The Big Bang Theory, managed to snag a starring role in both of 1989's big Christmas spectaculars. He plays Rusty in Christmas Vacation and had a role in John Hancock's less well-known film, Prancer.

WATCH: Throw Your Own Hallmark Christmas Movie Marathon Party

4. The Griswold children age differently than the rest of us

In both Vacation and European Vacation, Rusty is Audrey's older brother, the first born of the Griswold clan. At least it sure seems that way! However, in Christmas Vacation, Rusty somehow becomes Audrey's younger brother. Maybe it was a Christmas miracle?

5. The film has a beautiful connection to It's A Wonderful Life

Fans of the Christmas movie oeuvre may remember that a few scenes from Frank Capra's Christmas classic make an unexpected appearance in Christmas Vacation. The film, though, has another fun tie to It's a Wonderful Life. As Mental Floss points out, Frank Capra's grandson, Frank Capra III, is Christmas Vacation's assistant director.

6. The film's budget was massive.

Christmas Vacation is now one of the top 15 highest-grossing Christmas movies of all time, according to Forbes, who reports that the film brought in a whooping $71.32 million when it was released in 1989. The producers must have been relieved, because they dropped a jaw-dropping $27 million to make the film, Mental Floss reports.

7. Aunt Bethany may sound vaguely familiar

When Aunt Bethany says grace (well, the Pledge of Allegiance), some audience members may have recognized her voice—and for good reason. Aunt Bethany is played by actress Mae Questel who voiced both the iconic Betty Boop and Olive Oyl in the old Popeye cartoons.

8. Chevy Chase's favorite part of the movie is in the credits.

When video outlet, WhoSay, filmed Chase watching Christmas Vacation, he revealed his favorite part of the film comes during the opening credits, the Huffington Post reports. Specifically, when his name comes up above the title of the movie, which he said is "the definition of star." Maybe Santa can bring him a little humble pie for Christmas.

9. Chevy Chase still has the pajamas he wore in the film.

Chase told WhoSay that he still has Clark Griswold's pajamas and they aren't tucked into a drawer or memorabilia box. According to Chase's daughter, he used to wear them all the time, to which Chase added (jokingly, hopefully) that he still hasn't washed them.

10. The Griswold home may look familiar to fans of Bewitched—and Lethal Weapon

Remember when Clark gets locked in the attic and passes the time by watching old family movies? The footage includes an exterior shot of his childhood home, which Mental Floss notes is the same home as in the TV show Bewitched. And the fancy next door neighbor's house? That's the place that Murtaugh (Danny Glover's character) from Lethal Weapon called home. They are all located on a Warner Bros. backlot called Blondie Street, which is built to look like a suburban neighborhood.

11. There's a sequel

Christmas Vacation was a box office smash, so even though John Hughes wasn't a fan of sequels, the producers decided they need to cash in. That's how Christmas Vacation 2: Cousin Eddie's Island Adventure was born. The 2003 film stars Randy Quaid reprising his role as Cousin Eddie) when he and Catherine (played by Mariam Flynn) head to the South Pacific and are shipwrecked on an island—no RVs allowed.

12. The squirrel scene was pure chaos

In an interview with Rolling Stone, the movie's director revealed that the crew had hired an an animal trainer work with the dog and squirrel before that infamous chase scene. However, on the day of the shoot, the animal trainer had bad news: the trained squirrel they had hired for the part had died. The show had to go on, of course, but they had no choice but to use an untrained squirrel. As you can imagine, letting an untrained squirrel loose on a film set created utter chaos.