You know it's the holidays when "White Christmas" comes on the radio. The nostalgic song was written by Irving Berlin and introduced to a broad audience in the film Holiday Inn. The song was such a hit, that Berlin decided to write an entire movie around it. The film stars Danny Kaye and Bing Crosby as two soldiers-turned-entertainers, who fall for rising stars, the Haynes sisters, played by Rosemary Clooney and Vera-Ellen. The film follows the quartet to a little inn in Vermont, where all the mix-ups and misunderstandings are resolved as the snow falls on Christmas Eve. The film was a smash hit and is now a holiday classic, which should be no surprise considering the talent involved from the songwriter to the cast to the director, Michael Curtiz, who also directed a little film called Casablanca.

Here are a few things you might not know about the movie, even if you have seen White Christmas dozens of times:

In Holiday Inn, the song "White Christmas" was originally intended to be sung by one of the film's female leads. Instead, Berlin gave the song to Crosby and it became a classic.

Bing Crosby originally performed "White Christmas" on the radio show The Kraft Music Hall, before going on to perform it three times on screen. First in Holiday Inn and again in the 1946 film, Blue Skies, and finally in White Christmas.

The song "White Christmas" was not expected to be a hit. When it was performed in the film Holiday Inn, producers thought "Be Careful, It's My Heart" would be the chart topper.

When "White Christmas" won the Oscar for Original Song when it debuted in the film Holiday Inn, Irving Berlin became the only Oscar presenter to open the envelope and read his own name as the winner. "I'm glad to present the award. I've known him for a long time," he joked with the audience before presenting the award to himself.

Danny Kaye was the third choice to play Phil Davis. The role was originally intended for Fred Astaire, who starred with Crosby in Holiday Inn, however he was retired at the time and declined. Then producers asked Donald O'Connor, who had to pull out due to illness. Finally, Kaye was asked.

In typical Hollywood fashion, the film makes some funny age choices. On-screen couple of Rosemary Clooney and Bing Crosby had a 25-year age gap between them. Crosby was 51 at the film's release, and Clooney, 26. Vera-Ellen plays Clooney's younger sister, even though she's actually seven years older than Clooney. Dean Jagger played General Waverly as an old man, but in real life, Jagger is the same age as Crosby.

The Vermont inn where the film is set is a remodeled version of the Connecticut lodge from the movie, Holiday Inn. Sadly, it's impossible to stay at either of the quaint inns, since they were built on a Hollywood sound stage.

Irving Berlin wrote the song "Snow" years before White Christmas. It was originally called "Free" and had nothing to do with winter at all. Instead, it was what Rosemary Clooney called a "trunk song," a song that Berlin wrote, set aside and pulled out of the "trunk" when inspiration struck and rewritten for the occasion.

In the film, Judy Haynes shows Wallace and Davis a photo of her brother, Bennie. The man in the photo may have been a familiar face— actor Carl Switzer, better known as Alfalfa one of the Little Rascals from Our Gang.

The Haynes sisters told Bob and Phil that their brother was working "out of the country" in Alaska, which sounds strange to modern ears. However, when the film was released in 1954, Alaska wasn't part of the union, but merely a territory. It wasn't until 1959 that Alaska was admitted as a state.

Vera-Ellen, who played Judy Haynes in the film, was not known for her singing voice. Instead, her parts were performed by singer Trudy Stevens. Vera-Ellen's singing voice can only be heard once in the film, when all four stars reprise the song "Snow" while arriving at the Pine Tree railroad station.

There is no official White Christmas soundtrack, but there were two albums featuring songs from the film. The trouble arose, because Clooney was under contract with Columbia while the film studio was working with Decca. On the studio's album, Peggy Lee sings Clooney's songs. Later, Clooney released White Christmas songs on Columbia.

Bob Fosse was the uncredited choreographer for the movie, before moving on to strut his stuff in shows like Cabaret, Chicago, and All that Jazz.

Vera-Ellen wasn't much of a singer, but she was an incredible dancer. She became a Radio City Rockette at just 18-years old.

While Vera-Ellen had the moves, Rosemary Clooney did not, noting: "They could dub Vera's voice, but they couldn't dub my dancing."

Percy Helton, who plays the railroad conductor, appears in another holiday classic: Miracle on 34th Street where he plays the drunk Santa Claus at the beginning of the film.

The finale was re-shot as lark for the King and Queen of Greece who were visiting the set. There were a few things missing during the re-shoot, though: There was no film in the camera (because they had already shot the finale) and Bing Crosby was nowhere to be seen, having asked Clooney to "cover for him" before skipping out.

Kaye's sense of humor was responsible for one of the film's iconic scenes: Kaye was quite the comedian and when the director saw him goofing around with Crosby on set, he decided to add a scene to the film. The result was Wallace and Davis performing the Haynes' sisters "Sisters" act—and if you watch closely, you can see the stars laughing all the way through.