Marilyn got one-up on Olivier when she discovered that someone in the crew-she suspected it was Olivier himself- was running a book on how many takes she would need for a fairly tricky scene. Pianist Alan remembers: ‘Marilyn got wind of this and was not amused at the overt insult to her capabilities…”
She went home and studied hard so that on the day of shooting she was more than prepared. She delivered the line and then left the room, closing the door behind her as directed. However, within seconds the door flew open again and Marilyn stuck her head through the gap. ‘Pretty good huh?’ she exclaimed, before shutting the door for a final time. This line was not in the script and was an obvious dig at those who doubted her ability to do the scene. However, it fitted in so well that it wasn’t reshot and can now be seen in the final cut.
-Marilyn Monroe: Private and Confidential by Michelle Morgan