When Brian walks across the street as the cab pulls away, it is pouring rain in the street and on the sidewalk on the left. But the sidewalk on the right remains dry and rainless.
When Edward Burns' character, Michael is eating pizza during one of the montages, he's wearing his wedding ring. Burns probably forgot to take it off before shooting the scene.
In the rain scene of Patti and Brian in the evening after dining together, a white BMW cabriolet is seen under the rain with its roof open.
Patti writes a short story for the Paris review. Just before she puts the story into the envelope, a closeup at 55:05 shows three paragraphs. All of the three paragraphs are the same.
At 7:33 and 8:02, the audio is pig and prick respectively, but Kate's face moves differently.