Most of the time, a film's script is a story plan. It'll get passed through a whole line of professionals from screenwriters and producers to directors and studio executives to make sure that everyone's on the same page. But some of the most memorable moments in cinematic history were actually created off the page and on-the-spot. That's the magic of improvisation.



It could be a basic line, a simple gesture or even an entire monologue. Hell, we constantly quote and re-enact the moments ourselves like obsessed cult followers. And knowing that our favorite moment was actually off-script leaves us with a greater admiration for the actors.



To pull off such spontaneity, it takes a deep understanding of the synergy of the environment and ins-and-outs of the portrayed character. Sometimes the small addition produces something scary, sometimes funny and occasionally even pretty iconic. But no matter what, improvising shows an impressive initiative as a performer. Let's take a look at our top 10 greatest movie scenes where an actor decided to just go with the flow.

10. The Shining (1980)

Scene: Wendy Torrance (Shelley Duval) and her son Danny (Danny Lloyd) are hiding from their deranged husband and father Jack Torrance (Jack Nicholson) in a hotel bathroom. A window stuck half-open allows the son to escape outside, but still traps the mother in the room.



Jack slowly makes his way up the staircase with an axe and begins chopping through the door, complemented by wailing screams from Wendy. Jack then places his head to the jagged wooden opening and says, "Here's Johnny!"



Did you know: Nicholson actually decided to use that line because it was Ed McMahon's popular catchphrase introducing the highly non-threatening Johnny Carson on The Johnny Carson Show.

9. The Silence of the Lambs (1991)

Scene: Psychopathic Dr. Hannibal Lecter is in the middle of telling a story to FBI agent Clarice Starling (Jodie Foster) about his cannibalistic ventures; eating the liver of a census-taker "with some fava beans and a nice Chianti." Lecter then finishes with a freakish hissing sound, bringing the frightening scene to a revolting level.



Did you know:That famous hissing sound was actually something that Hopkins tried as a joke during rehearsals to spook Foster. Director Jonathan Demme decided to keep it to maximize the impact on audiences. Ultimately, Hopkins got less than 25 minutes of screen time in the film, but that was enough for him to earn an Academy Award and also deliver this skin-crawling moment.

8. Taxi Driver (1976)

Scene: Cab driver Travis Bickle (Robert De Niro) has reached a neurotic and sociopathic moment, where he decides to talk to himself in the mirror; pretending that he's confronting a politician that he plans to kill.



As he looks at his reflection, he repeatedly says "You talkin' to me?" before whipping out his gun. It shows just how much his character is losing his rationality and beginning to spiral out of control.



Did you know: De Niro pretty much improvised everything. The original script by Paul Schrader only said, "Travis talks to himself in the mirror." So the 34-year-old actor decided to take advantage of the character's mental state and perform one of the most classic one liners used today when walking by a mirror.

7. Saving Private Ryan (1998)

Scene: While waiting for an eventual German assault, Private Ryan (Matt Damon) and Captain Miller (Tom Hanks) sit down for a break on a destroyed French street. The characters swap stories about their lives back home and Ryan proceeds to talk about a funny story where his oldest brother gets caught making out with a girl in a barn. It's a moment of reflective happiness for the chuckling Ryan as he manages to vividly remember his family while in the middle of a hellish reality.



Did you know: That monologue from Damon wasn't in the script -- it was created completely off the cuff. While he wasn't really noticed for his overall performance as Ryan, Damon still managed to take control of the scene and deliver a spontaneous hit. And coming off of writing an Academy Award winning screenplay for Good Will Hunting, he was confident enough to use his storytelling abilities on the go.

6. Good Will Hunting (1997)

Scene: Whiz kid Will Hunting (Matt Damon) is at one of his many therapy sessions when therapist Sean Maguire (Robin Williams) decides to tell a personal story in order to get Hunter to better open up emotionally. He begins to recall a memory about his late wife and her flatulent habits. This causes Hunting to laugh hysterically.



Did you know: The entire story was made up by Williams mid-scene. Damon's laugh is actually genuine. And if you look closely, the camera shakes a tiny bit, most likely because the cameraman was laughing too. Williams earned his first and only Academy Award for his dramatic portrayal of the therapist, but still managed to plug in his well-known improvisational skills in a major moment.

5. Dumb And Dumber (1994)

Scene: Best buddies Lloyd Christmas (Jim Carrey) and Harry Dunne (Jeff Daniels) pick up a hitchhiker on a road trip. Little do they know that the hitchhiker is actually hitman Joe Mentalino (Mike Starr), hired to kill them. The joke's on him, though, because Mentalino doesn't know what he's in for.



Lloyd and Harry horse around endlessly, while the poor guy is stuck in the middle seat, trying to withstand the antics. He finally yells "Guys! Enough!" causing Lloyd and Harry to settle down for a moment. But just when the thug thinks that there's a calm ride ahead, Lloyd asks, "Hey, wanna hear the most annoying sound in the world?" and proceeds to yell in his ear.



Did you know: Yup, the entire scene evolved on the go. The original Farrelly Brothers script called for the two knuckleheads to test the hit man's nerves over an argument about jellybeans. But Carrey and Daniels ended up performing a whole bunch of craziness instead. Serious question: Did anyone really expect a duo like that to stick to an assigned dialogue?

4. Reservoir Dogs (1992)

Scene: Mr. Blonde, aka Vic Vega (Michael Madsen) is a thief who's torturing a police officer. The cop is tied up, has a duct-taped mouth and a couple of cuts on his face. But the whole scene is then pushed to a disturbing level.



After "Stuck in the Middle With You" begins to play on the radio, Vega breaks into a bit of a dance, before then approaching the tied up officer and cutting off his ear with a straight razor. Vega holds up the bloody organ in his hand and talks into the ear, saying, "Hey, what's going on? You hear that?"



Did you know: Director Quentin Tarantino never had anything scripted for Madsen to do after chopping off the prosthetic ear, so the actor just decided to improvise and add a quick -- and hilariously memorable -- comment.

3. Knocked Up (2007)

Scene: While on a car ride, Ben Stone (Seth Rogen) and Pete (Paul Rudd) perform a hilarious banter trying to make fun of each other in a really juvenile manner. After Pete says,"Know how I know you're gay?" the two of them go back and forth, repeating the line and filling in the blank with a comedic response.



The characters go through a bunch of answers -- from "You wear v-neck sweaters with nothing underneath" to "You still make Brokeback Mountain jokes."



Did you know: The entire dialogue is improvised by the two actors. In the DVD extra, the ad-libbed exchange runs for over six minutes. Rogen and Rudd first came up with the mindless idea on the set of 2005's The 40 Year-Old Virgin in a 30-second scene and then decided to continue the joke in Knocked Up. Comedy maestro Judd Apatow, who was the director and screenwriter for both projects, was confident in letting both guys run with their own creativity.

2. Raiders Of The Lost Ark (1981)

Scene: In the middle of a wild chase in the markets of Cairo, Indiana Jones (Harrison Ford) runs into a crowd, which disperses to reveal a black-robed warrior handling a large sword.



After facing some intimidating sword spinning, Jones decides to conserve some energy -- he puts away his whip, busts out a revolver and shoots the villain down. It's 95% badass, and 5% amusing.



Did you know: The scene was originally set to be an elaborate whip vs. sword fight. The swordsman rehearsed the sequence for weeks, but Ford got food poisoning the night before and couldn't perform the full action scene. So after consulting with director Steven Spielberg, the scene was changed to the iconic one-hit-wonder that it is today.

1. The Godfather (1972)

Scene: While Mafia caporegime Peter Clemenza (Richard Castellano) heads out to have Paulie Gatto (John Martino) killed, his wife also tells him to remember to pick up cannoli.



As a result, the murder takes place during the cannoli run. After Clemenza's henchman whacks Gatto in a parked car, the mafia man then instructs the lackey: "Leave the gun. Take the cannoli."



Did you know: The original crime script just asked for Castellano to say "Leave the gun." However, the actor decided to improvise some humor and play off the previous scene where his wife asks him to run the errand. With just one tiny tweak, Castellano created a boss of a line.