In the Hannukah/Christmas scene, Jessica takes a white ribbon from a gift and puts it around Helen's neck. In the next shot, the ribbon is gone.
The coffee mug in Joan's right hand and the position of Joan's arms switch repeatedly between shots when she is talking to Jessica in the office hallway.
When Jessica and Helen are outside on the street and they're eating ice cream and talking about the panhandlers, Jessica's purse disappears between shots.
In the first kiss scene on the street, Jessica's sweater moves up and down her left arm between elbow and shoulder between shots (we do not see her move the sweater).
The oranges disappear from Helen's hands at the fruit stand.
When Helen and Jessica are arguing outside the shop, you can see people in the background looking at them. Obviously these weren't extras, but bystanders who stopped on the street to watch the movie being shot.
During the opening credits, when Jessica is pouring sugar into her coffee from a yellow box, the Domino brand name on the front of the box is covered with white paper, but you can still clearly see the Domino brand on both the bottom and the side of the box.
Some shots during the wedding (when Jessica and Josh are up on the roof) are flipped (the text on a sign on the wall is reversed and the text on a sign on the inside of the door is also reversed).
When Helen and Jessica are arguing outside the shop, you can hear the loud footsteps of the camera operator shuffling back and forth to film the scene.
When Jessica and her mother are getting their bridesmaids dresses fitted, Helen is upset to learn that Jessica never mentioned her brother's upcoming wedding. But the wedding would surely have been discussed at the Shabbat dinner at the Steins' that Helen attended three months prior.