When Summer get's to the Cohen house to go to the party, her hair is straight and in a pony tail. Later at the party, when Summer is dressed as Wonder Woman, her hair is curled.
Ryan gets pulled over and hands over his license when asked for it. He is supposed to be only 15 years old and not legally allowed to have a driver license yet.
When Marissa enters the waiting room she places her jacket over the arm rest, when she reaches for a magazine her jacket is now next to her on the couch.
The length of Kirsten's hair changes throughout the episode. At the beginning her fringe is short (eg. when she is talking to Caleb) then at the Newport group Christmas party it is longer, then at the end of the episode her fringe is short again.
While talking with Ryan about Christmas, Marissa goes to her locker and opens it without unlocking it.