This is a great example of the value of what are often called, “table readings” of new screenplays. Most writers with a few scripts under their belt know to read their dialogue aloud before they show it to people, especially actors. Otherwise they may find their words not playing in situations where it will hurt them. Actors do not appreciate tripping over their tongues while delivering their lines in a group rehearsal, so writers should constantly test their stuff even before the first reader sees it.
Another interesting thing about this anecdote is that it concerns Billy Wilder, a director and writer who is known for his dialogue. But Wilder was relatively young, then, and had the disadvantage of speaking English as a second language, so he had a lot to learn. And, of course, he did... in spades. #