Improvising is the... uh... the best!

"HERE'S LOOKING AT YOU, KID" Casablanca is arguably the most oft-quoted film in cinema history, and perhaps the most famous line in it is one that Bogart would often say off-set to Bergman as he taught her how to play Poker between takes.

"YOU TALKIN' TO ME?" This is one that everyone should know by now. In the Taxi Driver screenplay, Scorsese had merely written: “Travis speaks to himself in the mirror.” The rest was De Niro magic.

"YOU'RE GONNA NEED A BIGGER BOAT..." Chief Brody gets his first face-to-face with the most menacing underwater foe. How does he react? With one of the most suitable, succinct and ad-libbed lines in cinema.

"HERE'S JOHNNY!" After chasing his family into a bathroom, Jack Nicholson utters a popular late night catchphrase from The Tonight Show starring Johnny Carson - and apparently going through 50 something doors in the process.

"I LOVE YOU." "I KNOW." When Leia declares her love for Han Solo, he responds with a cold, albeit comical, "I know". Originally, Ford was to respond with "I love you too", but he insisted this line was more suitable to Han's enigmatic charm.

NO TIME FOR SWORDS Originally, Indiana Jones was going to face-off against the flashy swordsman. But Ford was sick in real life and opted for the short way out. Little did he know his laziness would lead to one of the series most beloved moments.

"HEY, I'M WALKIN' HERE! I'M WALKIN' HERE!" Dustin Hoffman and Jon Voight are walking down the streets of NYC when a taxi unknowingly drives through their set. Hoffman, in character, responds perfectly as his character would.

"I ATE HIS LIVER WITH SOME FAVA BEANS AND A NICE CHIANTI. HSSSSSSSSS!" The final hiss, or slurp, or whatever you want to call it, delivered by Hopkins's Dr. Hannibal Lecter, still haunts our dreams to this day. And with it, Sir Anthony hiss-terically triumphed his way to an Oscar.

"GIVE ME THE KEYS..." In the scene when the criminals line up, the original intent was to establish a serious tone. But that didn't work, so instead we get a hilarious exchange of the criminals butchering their prescribed phrase.

"DON'T INTERRUPT ME, HONEY" In this 'game changer' of a scene, Lester Burnham finally stands up to his wife during dinner to claim back his manhood. Spacey proceeds to throw the asparagus at the wall rather than dropping it, which the script had originally written.

"I'M A ZIT, GET IT?" John Belushi was always full of surprises. For the cafeteria scene of Animal House, the script was essentially blank. They just let the man go and do what he does best.

"MY WIFE USED TO FART" Robin Williams had told a different story to Damon's character for each take of the scene. The one that makes it into the final cut shows the genuine reactions of both characters.

THE BARN STORY Matt Damon, though given little screen time in SPR, gives us a profound look into his character, Private Ryan, with a story that was completely ad-libbed. It's both funny and poignant, but above all feels true-to-life.

BASICALLY ALL OF HIS ORDERS Gunnery Sergeant Hartman (played by R. Lee Ermey, an actual former drill instructor) barks hilariously brutal remarks at his recruits for roughly 40 minutes, most of which was left unscripted.

"AH, KELLY CLARKSON!" Steve Carrell insisted that, for a more authentic feel - both literally and visually - he get his actual chest waxed. His reactions, along with his friends, are as genuine as they come.

"YOU WANNA' HEAR THE MOST ANNOYING SOUND IN THE WORLD?" As Harry and Lloyd embark on their road-trip, they ride along in the car of a hit man trying to kill them. Once in, Jim Carrey delivers the most annoying, unscripted sound ever, to the surprise of everyone along for the ride.

"WARRIORS, COME OUT TO PLAY-AY" For the Coney island confrontation scene, the director Walter Hill wanted David Patrick Kelly's character to, creatively, taunt The Warriors. A few bottle clinking later, and he delivers one of the more memorable singsong taunts in cinema history.

"MEIN FUHRER... I CAN WALK!" In a film that allowed Peter Sellers to literally be as versatile as he could, it is perhaps the final line he delivers, of both his and the film's, that many remember.

"HEADS UP!" John Malkovich was hit by a can that was actually thrown by a drunk extra, unscripted and unexpected. But I guess a movie about yourself encourages genuine reactions, right?

GESUNDHEIT When Alvy sneezes during the cocaine scene, it was originally unplanned but tested well with audiences and added the perfect element of slapstick to a rather serious scene.

"CAN YOU HEAR ME NOW?" Given free reign for dialogue in this scene, Mr. Blonde goes full Van Gogh on Marvin and ruins how we heard "Stuck in the Middle with You" forever. We're all listening to you now, Michael Madsen.

"WHY MALE MODELS?" Was he so into character? Or was he so forgetful? The latter admitted to the latter, but either way, his repetition and delivery of the line perfectly embodied our favorite dim-witted male fashion model.

"AND WHAT DID THAT PRODUCE? THE CUCKOO CLOCK" When Holly and Harry go up on that Ferris wheel, we are a given a brief, very Orson Welles-esque speech about Harry's insight on the history of mankind and the kind of progress (or lack thereof) that has been made.

"GAME OVER MAN, GAME OVER!" After coming up unsuccessful against the alien species, Bill Paxton's Private Hudson ad-libs a line that perfectly embodies his character's current state of mind.

"I DON'T CARE!" Gerard finally comes face to face with Richard Kimble, as the latter is at the edge of a waterfall drop. Tommy Lee Jones then delivers a dismissive, candid response to Kimble's plead for innocence.

NECKLACE CASE SNAPS SHUT When Edward (Gere) snapped the necklace case down on Vivian's (Roberts) fingers, we see the genuine reactions (including some wonderful laughter) from both people.

"LEAVE THE GUN, TAKE THE CANNOLI" The original line was merely "Leave the gun", but Richard S. Castellano wanted to reference the cannoli Clemenza's wife warned him not too forget. He's a husband first, and a mobster second.

"CINDERELLA STORY..." Though much of Caddyshack was improvised by Bill Murray, perhaps this story was the most memorable of moments. Ramis reportedly told Murray to pretend he was a kid pretending to be a commentator.

NEED A HAND? Audrey Hepburn's reaction to Gregory Peck's "bitten-off hand" in the 'Mouth of Truth' scene was genuine. Just before the cameras rolled, Peck quietly told director William Wyler that he was going to borrow a gag from comedian Red Skelton, and have his hand hidden up his sleeve when he pulled it out of the sculpture's mouth. Wyler agreed, but Hepburn was not told. When she saw Peck's "missing hand," she let out what she later described as "a good and proper scream."