When Harry and Lloyd are in the car, Lloyd asks if Harry wants to hear the most annoying sound in the world. This was not originally in the script (you can tell by the look on Jeff Daniels' face).
In the bar scene in Aspen, the line "No way... that's great. We've landed on the moon!" was not in the script but made up by Jim Carrey on the spot during shooting.
During filming, Jim Carrey stayed the night at the Stanley Hotel and requested to stay in the infamous room 217 (see Stephen King's: The Shining). According to the tour guide at the hotel, about three hours after Carrey went to sleep, he came running out of the room and left the hotel. To this day, he vows to never go back and won't tell anybody why. It is said to be because he saw the ghost of his grand dad.
Jim Carrey was initially offered $700,000 to appear in the film. However, the offer went in the same week when Ace Ventura: Pet Detective (1994) opened at number 1 in the US box office, so by the time Carrey's agents had renegotiated with the film's producers, his salary had upped itself to $7 million, almost half the film's budget.
According to the Farrelly brothers, Jeff Daniels wasn't wanted for the film, but Jim Carrey wanted him in it. In order to ensure a no from him, they offered Daniels $50,000 for the role. He accepted without any hesitation nor did he attempt to negotiate, despite insistence from his agent the film would "kill his career." By 1994, the film was Daniels' most successful.
Jim Carrey chipped his tooth years earlier, but had the cap removed for the film to make his character look more deranged.
When the film went to the top of the US box office, it gave Jim Carrey the distinction of being the first actor to have three films go straight to number one in one year (those films being this, The Mask (1994), and Ace Ventura: Pet Detective (1994)).
Jeff Daniels reportedly earned the role of Harry after the Farrelly Brothers remembered him from a Pepto Bismol commercial.
Although the ultimate travel goal was to reach Aspen Colorado, the actual town wanted too much money for film rights so many scenes were shot in nearby Breckenridge. The script however, was untouched. Certain shots were filmed in Estes Park, Colorado at The Stanley Hotel.
In order for Jeff Daniels to attain Harry's frizzy hair, during filming he was instructed to wash his hair only, and not to use conditioner, blow dry it, or even comb it.
The hotel, bar and Lamborghini scenes were shot at The Historical Stanley Hotel in Estes Park CO. The "We landed on the moon" photo in the bar remains on the wall. The Stanley was the inspiration for Stephen King's The Shining.
Production was shut down in Salt Lake City for a week when Jim Carrey had surgery for a gallstone.
The restaurant scene (with Seabass) was filmed in Ft. Morgan, Colorado. However filmmakers originally wanted to film this scene at a restaurant in Wiggins (about 15 miles west of Ft. Morgan) but after viewing the script the owner refused.
During the men's room stall scene, when Lloyd checks the time, the close-up of his wristwatch reveals it to be a "Casino Alarm Chronograph", suggesting it is a fake of the already, very inexpensive brand, Casio; it also lacks any of the dials found on a real chronographic timepiece, along with the 5, 6, and 7.
Bennett Yellin's initial draft of the script was apparently so disjointed that it had gained a negative reputation among film investors. After the script was re-written, it was pitched to producers under the fake title "A Power Tool Is Not a Toy", in order to get them to even read it.
Victoria Rowell is credited as Athletic Beauty. In the film, her character is called Beth Jordan and is an undercover FBI agent.
Among the many writings on the gas station bathroom stall are: "Why are you looking up here when the joke is in your hand?", "Bye Bye William Frawley", "NAMBLA Rules", and "Why the hell is everyone so goddamned angry?".
In the scene where Harry and Lloyd are escaping the "gas man", when they are running out to the dog van, there is a guy in the background urinating against a wall.
According to Jeff Daniels, none of the scenes between Jim Carrey and himself were filmed during the first week of production because the studio was fully prepared to replace him in the role, even going so far as to have a comedian on standby waiting to take the role. However, after viewing the dailies and constant insistence from Carrey that a real actor (as opposed to a comedian) play opposite him to "ground him", the studio ultimately allowed Daniels to keep the role.
The sports car Harry and Lloyd purchase is a Lamborghini Diablo. Supplied courtesy of Emich Lamborghini, Golden, Colorado - which has since closed down.
This is the second movie released in the same year in which Karen Duffy plays a character named Shay. She also played a character named Shay Stanley in Blank Check (1994). It was also the second movie released in the same year in which Jeff Daniels played a character named Harry. He also played Det. Harry Temple in Speed (1994).
The feature film debut for Peter and Bobby Farrelly. They said years later that the main reason they got the job was that Jim Carrey's breakthrough film role in "Ace Venture: Pet Detective" had been directed by someone who had never done a feature film before (Tom Shadyac) and after a positive first meeting with the Farrellys, Carrey decided to give them the job in hopes of replicating that success.
In the scene where Lloyd is driving and playing with Harry while he's sleeping, there is Aspen on the Left and Lincoln Nebraska on the right with Lloyd going to Lincoln Nebraska, Lincoln Nebraska is the place in Yes Man (2008) (also starring Jim Carry) is where he takes his friend to on there first trip together
The scene in which Harry tells Lloyd to throw salt over his shoulder is very similar to a scene in The Three Stooges short Beer and Pretzels (1933). Ted Healy throws a salt shaker over his shoulder, causing a fight. The Farrelly Brothers went on to direct The Three Stooges (2012).
The song Harry and Lloyd sing after picking up Mental is the same song the Griswolds sing when they begin their road trip to Wally World in Vacation.
During Lloyd Christmas's (Jim Carrey) dream sequence, when it looks like the chef has defeated him - he got brutally beaten up and literally had his head kicked in - Lloyd rises to his feet and says, "Eeuueh", to the chef who looks somewhat uneasy. Carrey also says, "Eeuueh", in The Mask (1994) released the same year as this film.
One of Jim Carrey's co-stars in this film, Lauren Holly plays Mary Swanson. In The Mask (1994) one of Carrey's co-stars, Cameron Diaz went on to play the titular character Mary in There's Something About Mary (1998). Incidentally Dumb and Dumber director Peter Farrelly co-directed it with his brother Bobby Farrelly. In their respective films both Carrey and Diaz sport outrageous hairstyles.
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