(at around 1 min) They are going to a birthday party and Nicole is not wearing her seat belt. A few seconds later they almost get into an accident with another vehicle, but Nicole is now wearing her seat belt.
In the party scene at the bowling alley when they start opening the presents, they open two: Becca's and the mom's present. After the argument about the gift they hand Izzy a big box with a safety pin wrapping paper. When they start bowling again, you can see the big box and Becca's gift fully wrapped on the table behind Izzy.
There were several scenes in which the characters went from wearing a seat belt to not wearing a seat belt, particularly when Nicole Kidman's character is watching the teen driver on the bus. The seat belt changes every few seconds from being on to being off.
When Becca walks into the room that is off of the kitchen to bring Izzy her crème brûlée, one can hear the door shut behind Becca, and in the next shot the door is completely shut. In the following shots of the Becca standing in front of the door during the beginning of her conversation with Izzy, the degree to which the door is shut changes noticeably from shot to shot.