As Jennifer, Stefanie Powers keeps her fingernails short. In all the closeups of Jennifer's hands, the fingernails are seen to be much longer.
The envelopes in Max's hand and then the tray, are not the same size. They keep moving in the tray, pointing one way, then another, then back to the original direction.
The lady moves to the bedroom to change from her suit to something more appealing. Only 20 seconds later she's wearing a negligee.
The villains' room is supposed to be number 314, but the camera pans up to about the sixth floor. It's probably stock footage.
The villainess chose not to lock the office door, which set up the entire plot.
The bad guy hangs around the gallery escorting people out instead of leaving immediately.
Affixing the million dollar stamp to a piece of mail, and then applying another stamp on top, no matter how carefully would severely depreciate its value.
Jennifer says that she needs to get her sweater, but she gets a shawl that matches her skirt.
The windows of the Hart's Mercedes are wide open, yet Jennifer is holding a lighter than air million dollar stamp as though it's worthless.