Star Wars: The Empire Strikes Back
In the scene where Princess Leia tells Hans Solo, “I love you,” we all saw how he responds. Fun fact: his response, “I know”, was unscripted. Yup, it is true! Fortunately, it was a perfect choice of words to include in the film. That moment in Star Wars: The Empire Strikes Back could easily be the most famous romantic dialogue of all time!
Young Frankenstein
Mel Brooks is one of the directors who promote ad libs in their work. The line, “What hump?” made the final cut of Young Frankenstein for that reason. It was Marty Feldman who went off the script and eventually pleasing everyone with the result.