Bill Murray, Dan Aykroyd are hilarious in original 'Ghostbusters' promo

We all know how the "Ghostbusters" story goes: Hilarious paranormal film with lots of slime and former "Saturday Night Live" stars Dan Aykroyd and Bill Murray hits big in 1984, spurs two sequels (one in 1989 and one forthcoming in 2021) and a reboot (in 2016), and becomes an instant classic.

But before it was released, nobody knew that was going to happen.

Which brings us to the very different cinema world of the early 1980s, where apparently stars of films that had all that classic potential still had to make promotional videos urging theater owners to actually show the movie. Turns out that both Akyroyd and Murray made just such an ad, and screenwriter/actor Todd Spence has thankfully shared it on Twitter (warning: there's one F-bomb):

"This is amazing. Dan Aykroyd and Bill Murray shot this short film for independent theater owners to sell them on showing GHOSTBUSTERS. And check out that original theme song too. Rad stuff," he wrote in the tweet. (A longer version lives here, on YouTube; the full version features unfinished scenes from the film and is 13 minutes long.)

In the video, the comedy duo speak to theater owners at the industry event ShoWest, which was held in Las Vegas, Nevada. The film was still being filmed in Burbank, California, when they made the clip, according to Spook Central: The Ghostbusters Companion webpage, so they had to talk it all up despite not having even wrapped.

"(T)his (movie) is gonna make 'E.T.' look like 'Raiders of the Lost Ark,' you know what I'm saying?" quips Murray, deadpan. "This is gonna be the kind of thing that your children are gonna say, 'Dad, I can look up to you now, but I never could before.' Isn't it worth it? Isn't it worth it? God, I mean, we made a lot of cheap movies for you guys that made a lot of money, but now we kind of spent a little more than we're supposed to."

Adds Aykroyd, "Columbia Pictures has spared no expense to make this... a fine science fiction comedy spectacle." He lets everyone know it's a PG film, after which Murray says that stands for "pink gums."

"I mean, the people who can come in and eat and eat and eat that sugar and popcorn and those soft drinks," says Murray.

"And the thickness of the sucrose syrup on the floors of your theaters after this film is over, after every screening. I mean, we're talking inches and inches," says Aykroyd.

But if that wasn't enough, the video features one more gem toward the end — the debut of the "Ghostbusters" theme song, and it goes a little something like this:

"Front line, anytime/ Take it right to the Ghostbusters/ Cool heads under fire/ Never mess with the Ghostbusters"

Now, wait a minute. What happened to Ray Parker Jr.? To "who you gonna call"? Well, it turns out that the movie wasn't the only thing that wasn't totally finished — there was more than one potential theme song being considered. The one in the video is from Glenn Hughes and Pat Thrall, and it can be heard in its entirety here.

Fortunately, everything ultimately worked out like it was supposed to: Theater owners loved "Ghostbusters" almost as much as the audience, and Ray Parker Jr. came up with his signature tune and line about who you should call in case of paranormal infestation. And now we all know who to call: Ghostbusters!