Sometimes, you just got to make it up as you go along. At least, that's what Harrison Ford did in 1980's The Empire Strikes Back. Originally, in the now famous scene where Han is about to be frozen in carbonite, the script contained a scene in which Princess Leia (Played by Carrie Fisher) professed her love to Han Solo (Played by Ford), with Han replying "I love you too." However, Ford felt the characterization was not being used effectively, and director Irvin Kershner agreed. So, ater several takes, the director told the actor to improvise on the spot, and Ford changed Solo's line to "I know." And now, that line is legendary...and pretty smooth.
A line that will never be greenlighted in modern PC world.