Margaret Ford takes her smokes from a package of unfiltered "stubby" Camels, but the actual cigarettes she uses are longer (probably Pall Malls) so they'll "read" better on screen.
Margaret asks the House of Games's barman to call Mike out. Then he enters in the game room and closes the door. We don't see him comes back. So Mike opens the door and comes to talk her. During the conversation we don't see the barman behind the counter. But after Mike went to the game room, the barman appears behind the counter.
When Mike is dressing in the hotel room, the narrow (back) side of his necktie is clearly three inches too long when he finishes. One edit later, wardrobe has obviously corrected the error.
Towards the end of the film, Margaret Ford returns to her private office and cuts herself. Several drops of blood fall on the cover label of a dossier lying on the desk. In subsequent shots, the blood stain jumps down the label and finally ends up on the back cover, leaving the label clean.
When Margaret is talking with Maria outside at the picnic table she lights a cigarette with her right hand and in the process of removing the cigarette from her mouth it changes to her left hand.
In the restaurant, Margaret says to her mentor that her patient called the animal in her dream a lirg and that lirg is the inverse of girl. That's incorrect as the inverse (actually the reverse) of girl would be lrig, not lirg.
When Margaret fires the final three shots at Mike the gun is clearly aiming far too high to get even close to hitting him.