Continuity mistake: In the scene where Erica and Zoe are in the kitchen and start hearing music, Zoe starts a mock calling, moving both her hands, in the shot from the front both her hands are empty the shot changes to her back and she has a glass in her hand.
Other mistake: Harry (Jack Nicholson) tells Erica (Diane Keaton) that he only sees her in turtleneck tops. However, when he first meets Erica and Zoe in Erica's kitchen, she is wearing a scoop neck.
Continuity mistake: In the scene of the freeze, where Erica and Harry first meet, see Marin's hair on her forehead change several times during close-ups.
Continuity mistake: When Keaton and Nicholson argue outside the restaurant and Keaton confesses she is in love with him, in certain closeups Keaton holds her head with both hands. When the camera cuts to Nicholson's face, you see her back and her arms are down. This happens twice during the scene.
Continuity mistake: In the scene at Le Grand Colbert restaurant in France the white rose in the vase on the table varies between a state of full bloom and being a small closed bud from shot to shot.
Continuity mistake: When Harry and Erica are having a picnic at the beach the sun light changes from shot to shot.
Deliberate mistake: When Harry is seen stepping outside of his hotel the evening after he arrives in Paris, behind him is the familiar Eiffel Tower gloriously illuminated against the night sky. Frequent Paris visitors or residents might recognise the hotel as the Plaza Athenee - to see the Eiffel Tower from there you'd need to be looking in the opposite direction from what we're shown.
Factual error: The audition scene for Erica's play would never take place in the theatre. Auditions and rehearsals are held in rehearsal halls, not the theatre. Yet they show the sets already built and installed, lighting and effects in place, and they reference the costumes being ready. This does not happen until the show is close to opening.
Continuity mistake: When Harry and Erica go to "sleep" together, they're on particular sides of the bed. The next morning, they're on opposite sides of the bed when they wake up.
Other mistake: When Erica and Harry are walking along the beach, picking up stones, and then Erica checks her watch because of her upcoming Dinner Date, she's not wearing her glasses, which she seems to need every other time she needs to look at the clock later in the movie.
Continuity mistake: When Harry and Erica lay in bed to "sleep" together, they are each sleeping in certain sides of the bed. The next morning, they've switched places in the bed.
Continuity mistake: When a plate comes suddenly crashing to the ground, Erica is seen standing in her kitchen, above a white plate with a few bits of leftovers on that cracked plate. She is arguing with her sister about the "appropriateness" of the relationship between Harry and her daughter. As she bends down to pick it up, the plate is suddenly filled with red tomatoes and a heap of leftovers.
Answer: When they were trying to see what time it was the morning after they had slept together.