Revealing mistake: When Marin and Jack Nicholson first enter her mother's house, Marin is wearing white pants, and it is noticeable that she has a thong on. When she gets into bed with Jack, she is in full underwear.
Revealing mistake: Right before Jack Nicholson sees Diane Keaton naked, there are shots of Keaton getting undressed. There is a close up of swollen feet that you can see are obviously not Diane Keaton's. The far shot shows her with smaller feet and legs.
Revealing mistake: In the scene where Harry and Erica are walking on the beach, Harry bends down and supposedly picks up a black rock to give to Erica. However, the viewer can see Harry take an object out from his left pocket and, while concealing it with his left hand, transfer it over to his right hand as he bends down and pretends to pick up the rock from the beach.
Revealing mistake: In the scene where Jack Nicholson leaves the Hamptons hospital and collapses in the parking lot, a palm tree can be seen in the background. There are no palm trees on Long Island.
Answer: When they were trying to see what time it was the morning after they had slept together.