Continuity mistake: At the very end when Joe and Kathleen start to kiss, in the close up of the kiss, you can see a patio umbrella (like at an outdoor cafe) being opened in the background. The next shot we see Joe and Kathleen from far away, and the camera pans up to the sky. If you look in the background during the pan, you can see the umbrella being opened again. (01:54:30)
Continuity mistake: When Meg Ryan's boyfriend is showing her his new typewriter, the amount of paper fed into the typewriter changes between shots. From far away about a quarter of the paper is fed through, but when the shot closes half the paper is fed through, the shot widens again and only a quarter is fed through. (00:19:10)ACertainShadeofGreen
Continuity mistake: Brinkley, Joe's male dog, is obviously a smaller female dog, and she is played by two different dogs. One dog has longer hair than the other. The two dogs keep switching back and forth. The dog(s) never seem to respond to the computer screen or any other directed area, they are firmly focused on their trainer.
Revealing mistake: When Fox is on the boat with his dad, there is no rocking happening. It's as if they are on dry land when they are not supposed to be.
Revealing mistake: When Kathleen leaves Joe on the street and goes home to get ready to meet NY152 in the park, she uses her key to unlock the deadbolt; you can hear it click. But the place where she puts the key is a flat, blank space on the door; there is no key hole.