Directed by Todd Phillips from a script penned by both Jon Lucas and Scott Moore, The Hangover is sometimes seen as one of the funniest movies ever made. Its cast is nearly as famous as the film itself, with massive names like Bradley Cooper, Ed Helms, and Zach Galifianakis. On top of being widely considered among the best comedies of the past two decades, this feature also soared at the worldwide box office, and even spawned two sequels that released in the subsequent decade.

It wasn’t suspected to succeed, however. Studios were hesitant to pick up the script, and multiple other actors were signed on to perform before they landed on one of the funniest casts to ever be assembled. The runaway popularity of The Hangover caught everyone off guard, with the positive response from critics coming as just as much a surprise. And given the results at the box office and subsequent name value accrued therefrom, there’s no doubt that everyone involved with the production has endless gratitude for making comedy movie history.

All that said: the filming process of The Hangover involved great controversy, emotional turmoil for its actors, and some hilarious behind-the-scenes stories that rival the comedic value of the film itself.

The cast and crew were forced to think on their feet on various occasions, with many famous moments from the film being born out of improvisation. In hindsight, this provided a tremendous sense of spontaneity and ridiculousness to an already off-the-wall production.

The Hangover’s Improvisation
Warner Bros. 

Of course, a great portion of the footage was filmed on location at Caesars Palace, a hotel and casino in Las Vegas. However, the suite in the film that was destroyed by the characters was actually built on a soundstage. This is a fairly basic resolution for general film production, but one that showcases the commitment of their ideas, nonetheless. Messing up the room was essential to the plot, but perhaps not to that extent.

Related: Ed Helms Says The Hangover Fame Left Him Panicked and Overwhelmed

Individual moments were improvised, as well; take Stu’s song, for instance. Among the most indelible sequences of the film as a whole was Ed Helms providing his dulcet vocal intonations while tickling the ivory. It’s a famous scene, but plenty of fans fail to realize that it was actually improvised entirely. There are several more instances, like actor Ken Jeong jumping on Bradley Cooper’s neck when the former was found nude in the trunk of a car. The stunt was pulled off with Cooper’s immediate blessings.

And sticking with Jeong: the Police in Los Angeles were not particularly pleased with his streaks of nudity. They even threatened to shut down production entirely, leading the team to again think on their feet. They built a wall of blackout cloth to cover Jeong during his scenes, with one more notable instance of improvisation coming toward the end of the film.

Finding the camera full of pictures as the end credits scene is an idea attributed to American screenwriter Jeremy Garelick, and was not part of the script. Of course, plenty of these instances of improvisation involve wild stunts and absurd dialogue for all of Las Vegas to see and hear. And there could never have been a better cast to pull everything off.

The Commitment of the Actors
Warner Bros.

Off the bat, it’s worth noting that Ed Helms had a dental implant as a teenager that was removed for filming. The chipped tooth of his character Stu wasn’t prosthetics or visual effects, but instead Helms revealing to the world his true toothy nature. Not the biggest of deals, but Helms did take a couple of other hits for the team along the way when filming The Hangover.

In the scene where Mr. Chow rams his car into that of the main characters, Stu was pulled out of a window. He took decent damage to his legs in the process, and in the subsequent scene.

This was a very successful franchise, with moments aplenty of public embarrassment. Throughout the shoot, these famous actors walked around Vegas in torn clothing with scratches obscuring the makeup on their face. A few members of the cast such as Cooper have stated their disbelief at the lack of attention this brought.

Related: Best Todd Phillips Movies, Ranked

Of course, Jeong couldn’t avoid legal scrutiny during his sequence of streaking. But that was his idea, to be nude, even suggesting it to Phillips and, upon the agreement from the director, then asking his wife for permission. He was down for the cause. On the other hand, Galifianakis was mortified with a certain scene. You might recall a sequence in an elevator at Caesars where a woman performs fellatio on the actor. This was filmed with a prosthesis, but Galifianakis nonetheless left the exchange discountenanced, comically telling MTV:

I got talked into it. I offered Todd’s assistant $1,000 if he could convince Todd to not have that in the movie.

Of course, the image is in the film, and audiences around the world are better off for it. And none of this was to even mention Mike Tyson and his tiger. Just imagining these stories from behind the scenes playing out in real time creates a sense of comedic poetry regarding The Hangover as a whole. The actors will never forget their time on set — nor should audiences take their work for granted. They must have looked pretty silly, though.