Doris Day's cameltoe
This is way too obvious to be accidental. At 38:21 into the movie, she swings both legs over a typewriter case while sitting on the desk. I couldn't've been the only one to notice this, and lo-and-behold:
http://forum.adultdvdtalk.com/doris-day-cameltoe
That screenshot does NOT do it credit, but it's there all right.
Total surprise, and incredibly, David Niven does a fantastic job of not looking (or noticing) at all.