Marilyn's mole
Her mole definitely delivered a performance of its own in this film. At first, it was on her cheek like usual, but then, midway through, it disappears, and by the third act, it is below her lips on the bottom left.
I actually think it is better there than on her cheek. The only other Marilyn film where her mole was below her lips on the bottom left was Some Like it Hot, which came before this.