Talk about an underground classic. Tremors—easily the greatest subterranean monster movie ever made—turned 25 this month. So, we’ve dug up some trivia that’ll help get you in the mood for an anniversary screening. Just watch your step…

1. The Premise Came to Screenwriter S. S. Wilson During a Rocky, Southwestern Hike.

Giant, worm-like beasts terrorizing Nevada. Now there’s an idea as wild as the West. The Tremors franchise has proved remarkably successful, having spawned a short-lived TV series, a prequel, and two sequels (with a third coming this October). But how did it all begin? According to Wilson, we can thank some scrap paper and the Armed Forces’ film division.

“I had a job working as an editor at a navy base in the middle of the Mojave Desert,” he explains. “On weekends, when they weren’t shooting at the gunnery ranges, I was allowed to go hiking out there. One day, while climbing over large boulders, I had a thought. ‘What if something was under the ground and I couldn’t get off this rock?’” Wilson jotted his idea down, pursued it years later, and the rest is history.

2. Saturday Night Live Forced the Movie to Change its Name.

Tremors (1990) began pre-production with the working title “Land Sharks.” However, upon realizing that SNL had already unleashed a recurring character called LandShark to spoof Jaws (1975), Wilson and company decided to change the movie's name.

3. A Menagerie of Real-Life Animals Inspired the Creatures’ Design.

The real stars of Tremors are four grotesque carnivores called “graboids.” Though there’s nothing quite like them in the animal kingdom, Mother Nature still played a big role in bringing these things to life. Special effects artists Alec Gillis and Tom Woodruff Jr. threw bits and pieces of such real-world critters as elephants, crocodiles, dinosaurs, rhinos, slugs, and catfish into their graboid sketches. You may have noticed that, weirdly, this list excludes earthworms, which the pair found “very boring.”

4. Tremors, Gladiator (2000), and Iron Man (2008) Share a Key Filming Location

Alabama Hills in Lone Pine, California, has also provided backdrops for Star Trek V (1989), Dinosaur (2000), Man of Steel (2013) and hundreds of other movies. In Tremors, these majestic mountains border Perfection, Nevada, a fictional near-ghost town.

5. Some Early Graboid Concept Art Was Deemed “Too Phallic.”

Gillis and Woodruff dropped the idea of a turtle-like neck when somebody alleged that their monster’s blubbery folds resembled “foreskin.” As Gillis recalls, producer Gale Ann Hurd “said that when we would fax the drawings over, all the women in [her] office would pass ‘em around and giggle.”

6. Like Many PG-13 Movies, Tremors Gets Away with a Solitary F-Bomb.

Fun fact: The Motion Picture Association of America—best-known for its (in)famous ratings system—allows “one nonsexual F word per script” in PG-13 films. Tremors takes advantage at the 34:07-mark, when Val tells off a recently-killed Graboid.

7. Wilson and Co-writer Brent Maddock Thought It’d Be More Realistic if Their Film Never Revealed Where these Graboids Came From.

Wilson in particular was fed up with the Sci-Fi genre’s standard monster origin clichés. “[They’re] either radioactive, or they’re a biological experiment, or they’re from outer space, or they’ve always been there," he said. "Those are the only choices you have.” Thus, Tremors offers no information about its creatures’ beginnings (though later films claimed the man-eaters were prehistoric reptiles).

8. It was Reba McEntire’s First Movie.

McEntire postponed her honeymoon with fellow musician Narvel Blackstock until after Tremors finished shooting to play the fearless, gun-toting Heather Gummer.

9. Only One Full-Length Graboid Model Was Constructed.

After an overzealous graboid fatally crashes into a cement wall, our heroes Valentine “Val” McGee (Kevin Bacon), Earl Bassett (Fred Ward), and Rhonda LeBeck (Finn Carter) unearth the monster’s corpse. What they actually expose is a massive, one-of-a-kind dummy you can see in all its pebbly glory above.

10. The Car Scene Was Supposed to Be a Lot More Explicit.

Horror’s all about what you don’t see. During one chilling sequence, a hungry graboid devours a middle-aged doctor, traps his petrified wife inside their station wagon, and drags the entire vehicle underground. At first, director Ron Underwood planned on recording the car as it sank into a pit filled with vermiculite, an earthy, “dirt-like” substance. But, maddeningly, this material hardened without warning and his crew was forced to improvise.

Their solution? Subtlety. Following a brief struggle, the finished movie cuts to a distant, wide-action shot of two headlight beams shining upwards into a starry sky before flickering out. The insinuation of a deadly off-screen burial was pulled off with some last-minute imagination.

11. The “Golden Oldie” Val Hears is “Dropkick Me, Jesus (Through the Goalposts of Life)” by Bobby Bare.

Yes, that’s an actual country song title. Val and Earl discover what happened to the good doctor’s car when this 1977 Grammy nominee starts blaring from its (now-submerged) radio.

12. Chinese-American Actor Victor Wong (Walter Chang) Came up With His Character’s Last Name.

In Tremors, Tremors 3 (2001), and Tremors: The Series (2003), a lot of action unfolds around Chang’s Market (located in “downtown” Perfection). At first, the original film’s script called for a Vietnamese store owner, but when Wong was cast, his role’s nationality was tweaked. Upon getting asked to suggest a Chinese last name, Wong proposed “Chang.”

13. The Flick’s Original Intro Wound Up on the Cutting Room Floor.

Tremors opens with Kevin Bacon peeing into a canyon. Admittedly, that’s hard to top. Still, a much darker beginning—wherein the mule of Perfection’s town drunk is gobbled up inside his rickety, wooden pen—was shot but ultimately deleted.

14. Universal Pictures Chose to Replace Most of the Soundtrack.

A strong score with a western twang spices up this movie’s unique flavor. But did you know that Ernest Troost—who was officially credited with composing it—actually wrote relatively little of the finished product? Instead, Robert Folk created the lion’s share after Troost’s offerings were largely removed. “He must have had a very good lawyer,” Folk says, “because the provision in his contract stated, that if any of his music were used, that he would have screen credit… I was asked [if I wanted to share] screen credit and I really didn’t.”

15. Michael Gross Started Filming One Day After Finishing the Beloved Sitcom Family Ties.

Kindly Mr. Keaton of Family Ties fame couldn’t be more different from Tremors’ breakout character. Gross’ tenure as Burt Gummer—a no-nonsense, gun-toting, and often anti-social survivalist—began less than 24 hours after the show which made him famous had its wrap party. On a related note, we’ll apparently be seeing plenty of Gross in the upcoming Tremors 5.

16. A Tentacle Hand Puppet Was Grudgingly-Built, Yet Widely-Used.

Three mechanical, full-length, state-of-the-art tentacles and a slightly-shorter “attack” version all earn significant screen time. But Maddock felt something rather basic was missing: a hand puppet. At first, the effects artists didn’t take his suggestion very seriously, but as the simple prop proved increasingly helpful during difficult shots, their tune changed.

17. Tremors Gave Kevin Bacon Severe Sleepwalking Nightmares.

For years, Bacon considered Tremors a low point in his professional career. “I broke down and fell to the sidewalk, screaming to my pregnant wife, ‘I can’t believe I’m doing a movie about underground worms!’” he told The Telegraph.

He’s since warmed up to the movie, but still remembers “Having these crazy dreams about monsters” while filming. Those nightmares also led to some very bizarre evenings for Bacon’s then-pregnant wife, Kyra Sedgwick. “I would pick her up,” he said, “and sleep-walk and carry her out onto the street… She’d be like ‘Honey, honey, honey, you’re asleep!’ and I’d say ‘No! I’ve gotta get you out of here!”

18. Underwood Nearly Appeared as a Cross-Gendered Stunt-Double.

Directors' cameos don’t get much stranger than this. When the time came to film Tremors’ climax, Finn Carter’s stunt double was a no-show. So Underwood grabbed a wig and jumped into the fray himself for a few frames he later cut.

19. The Moving Graboid “Humps” Were Achieved With a Boat Buoy.

Insert Jaws theme here: By chaining these maritime units to a truck and dragging them through underground troughs, the team created an ominous tunneling effect complete with rapidly flying dirt during key action scenes.

20. Tremors’ Ending Was Altered When Test Audiences Reacted Poorly.

Val and Earl spend the entire movie pining for the greener pastures of a nearby town named Bixby. Yet, as their graboid-slaying quest unfolds, Val finds himself growing close to Rhonda. Naturally, pre-launch viewers hoped they’d kiss after vanquishing the monsters. Instead, Tremors originally ended with the two men driving to Bixby before getting a change of heart and turning around. Clearly, this wouldn’t do—or at least, that's how Underwood’s test audience felt. The last few minutes were then swiftly re-shot to include that requisite smooch.

21. The SyFy Channel Later Gave Graboids a Faux Scientific Name.

Before Tremors: The Series debuted on SyFy, a (now-defunct) tie-in website claimed that, following the first film’s events, scientists coined the Latin name Caederus mexicana for this newfound species.

22. Slither (2006) Includes a Sneaky Tremors Reference.

In an obvious nod to Fred Ward, the heroine in this campy delight teaches at “Earl Bassett Community School.”

23. There’s a Tremors Exhibit at the Lone Pine Film History Museum.

Their wonderful display includes an enormous prop graboid head and a scale model of Chang’s Market. Next time you’re in eastern California, be sure to check it out!

Additional Sources: “The Making of Tremors,” Collector’s Edition DVD Bonus Feature; The Ultimate Tremors FAQ