When Jonathan brings out beer at the end of the story, the glasses have a large amount of froth at the top. In the next shot, the froth is almost gone. In the next shot, the froth has returned.
As Jennifer, Stefanie Powers keeps her fingernails rather short, this can be seen when she removes a note from a magnetic clip on the refrigerator. The thumbnails seen holding the note while she reads it are much longer.
In the second-to-last scene, during the reception, a brunette extra in a pink blouse and black skirt is seen standing in the background behind Jennifer. In other shots, she's also seen sitting in front of the table where Jonathan, Raymond, and Jeremy are.
No button lights up on the phone in the distributor's office when the phone rings.
There's an obvious stunt double for the lady fighting with Jennifer.
The tray of fruit in the long shot is not the same as that in the close up.
When Jonathan and Jennifer are at Dumont and they notice the shelf above them is going to fall, it's obvious that the actors have been replaced by stunt performers: the male isn't wearing Jonathan's pinkie ring on the right hand and the woman isn't wearing the rings that Jennifer wears on her ring finger and pinkie.