Movie fans will never know how many writers, producers, or directors shape a movie script before it actually comes time to start filming. But no matter how meticulously things are prepared, there's something to be said for chasing the inspiration or ideas that pop up on set. And sometimes, lines or scenes improvised on the spot can not only work, but become instant classics.

Here are Screen Rant's 10 Amazing Movie Scenes That Were Completely Improvised.

The Avengers: Age of Ultron

Avengers Ultron Improvised Scene

When the Avengers characters Hawkeye and Quicksilver first crossed paths, they did so as enemies (with the latter giving the heroic archer a serious wound). Even so, they wound up as allies by the movie's final fight against the forces of Ultron. But that didn't stop the archer from being tempted to take him down. When Quicksilver delivers a quip at Hawkeye's expense before speeding off with his sister, the archer draws back his bow, telling himself that "nobody would know... nobody." The gag was one of the funniest in the film, and it was improvised by Jeremy Renner during shooting.

Guardians of the Galaxy

Rocket Raccoon looks on in Guardians of the Galaxy

Bradley Cooper recorded the voice for Rocket Raccoon once filming on Gurdians of the Galaxy had wrapped, but it was director James Gunn's brother Sean who played the mercenary on set (and landed a small role as one of Yondu's Ravagers). When the rest of the team are finally agreeing to head off on their final suicide mission, Gunn apparently ended up putting his co-stars into tears. That was before he improvised the line that ended up being used to bring the entire scene to a close: "We're all standing now. Bunch of jackasses, standing in a circle."

Independence Day

Independence Day Improvised Unscripted

Sometimes, an unscripted line can fit the scene so perfectly, audiences never even think that it could have been thought up on the spot. But one of Independence Day's most quotable lines came directly from the mind of Will Smith, as his fighter pilot is dragging an unconscious alien across the salt flats. Stuck in the middle of nowhere, he lets all his frustration out on his would-be alien killer. The extra twist was that nobody warned the crew (or actor) that Utah's Great Salt Lake is actually home to millions of brine shrimp - which wound up rotting just below the sandy crust once the lake dries out. The result: Will Smith's final outburst - "and what the hell is that smell?!" - had nothing to do with the alien, just the location.

Jurassic World

Jake Johnson in 'Jurassic World'

As serious as a runaway dinosaur might be, the Jurassic Park sequel found time for plenty of humor. But when the oddball tech Lowery (Jake Johnson) decides to play the hero and stay behind, partly to impress his female coworker (Lauren Lapkus), he gets shut down fast - learning in a heartbeat that she's had a boyfriend the entire time. The line was improvised by Lapkus, and the two playing out the surprise reveal made it into the final cut.

The Wolf of Wall Street

Matthew McConaughey in Wolf of Wall Street

Matthew McConaughey has become famous for doing everything a little bit differently, but sometimes, his odd behavior behind the camera makes it in front. When audiences first saw his Wolf of Wall Street character start humming and beating his chest in a crowded restaurant, they were just as confused as Leonardo DiCaprio. The ritual was one McConaughey would actually practice before shoots - when his co-star caught it, he asked if they could try it during the scene. Even so, you can spot DiCpario cracking up, and even looking to his director and crew as the ritual builds.

The LEGO Movie

LEGO Movie Unscripted Improvised

Given how famous Morgan Freeman's voice has become, it shouldn't surprise anyone that even his outtakes are too good to leave out. When The LEGO Movie's Vitruvius is introducing Emmet to the rest of the Master Builders, a mix-up with Gandalf and Dumbledore leads to a quick one-liner: "Ah, we gotta write all that down 'cause I'm not gonna remember any of it, but here we go..." The line wasn't performed, but actually spoken by Freeman to the directors during his time in the recording booth. Obviously, they found the perfect place to fit in the glimpse of Freeman's sense of humor.

Star Trek

Star Trek Movie Spock Improvised Unscripted

The big screen reboot of Star Trek managed to excite a new generation of moviegoers, while doing right by fans of the original - and Leonard Nimoy's appearance as the original Spock was a big part of it. As proof that the classics are always to be trusted, Nimoy asked J.J. Abrams if he could improvise a final line after seeing Kirk given command of the Enterprise. In the script, Spock was intended to give the scene an approving smile and nothing else. Instead, Nimoy uttered a simple phrase: "Thrusters on full..." It was a perfect moment, sending the movie towards its close, and letting Spock - and Nimoy - hand the franchise off to a new generation with a single order.

True Lies

True Lies Unscripted Movie Scene

James Cameron's big-budget spy thriller had a ton of stunts, but it was Jamie Lee Curtis' relentless workout plan that made headlines, insisting that she perform a sultry dance for her on-screen husband personally (body doubles be damned). She got just as carried away as her character, apparently, since her fall to the floor was completely unscripted - you can even watch as Arnold Schwarzenegger jumps up to help before realizing she's pushing through, and sliding back into the scene as best he can.

Teenage Mutant Ninja Turtles

Ninja Turtles Elevator Unscripted Improvised

Fans didn't have high hopes for the movie reboot of the heroes in the half-shell, but the modern Ninja Turtles kept the teenage energy completely intact. Some of that is due to the actual actors playing the part, and the decision to bring their own personalities into the film. When the producer noticed the stars goofing around and freestyle beatboxing between takes, he insisted they do the same for the actual movie. It became one of the best scenes in the movie, with the animators turning the improvised song into a CG masterpiece.

Captain America: The First Avengers

Captain America Shirtless Unscripted Peggy

Marvel relied on some risky special effects to bring their star soldier to life prior to his superhero rebirth. But even if star Chris Evans' face was added onto a smaller actor to start, the audience couldn't prepare themselves for the musclebound supersoldier that emerged from the experimental procedure - and neither could Evans' co-star, Hayley Atwell. The actress has admitted that she's genuinely flustered in the scene, with her reactions - and the need to actually touch Evans' pecs - all completely unscripted. Can you blame her?

Conclusion

Those are the famous, iconic, or hilarious movie moments that have luck and improv to thank, but what favorites of yours have we missed? Let us know in the comments, and subscribe to our YouTube channel so you don't miss our next installment!