Star Wars Episode 5: The Empire Strikes Back - Read My Lips
When in the space slug a tremor rocks Han's ship causing Leia to fall into Han's lap, watch Han's lips when Leia says, "Captain, being held by you is hardly enough to get me excited."
Ok, this is happening because Carrie Fisher was fighting a drug addiction at the time and could not memorize all of her lines, Harrison Ford is helping her out.
I went back and watched this suspect scene and agree that Harrison Ford is mouthing the lines, but do you really think he was prompting Carrie Fisher? First of all, we can hear Carrie but not Harrison. Secondly, he is mouthing the lines in exact sync with her and am almost sure that, at one point, she says the line before he mouths it. If he were giving her the lines, there should be at least a half a second interval before she repeats it. I have heard that he prompts her in several scenes, but this is the only time I could tell that he was mouthing her lines.
Well, maybe he's mouthing the words to assure her that she is saying the right thing. And maybe Harrison did say them and they just edited out his voice. As for the "I know" thing, that came about because Ford thought that saying "I love you too" was a cliched line and wanted to do something different.
A stoned Carrie huh? Yeah I've heard of that one too, but somehow I find it hard to believe she would have been allowed on set if she was so bad that she couldn't remember her lines!
And in any case, she hardly looks stoned in this scene!
In fact, rumor has the now famous exchange just before Han is put into carbon freeze: Leia: I love you, Han: I know... was the result of an irritated Harrison Ford attempting to finish off a scene that a clearly stoned Carrie Fisher kept screwing up.