As Joan and Roger hug in her apartment, the position of her head keeps changing between shots.
At approx 44 1/2 minutes when Don is talking to Fay at his apartment, her pearl necklace first appears half in her dress neckline and half out. In the next cut back to Fay, the entire necklace appears on the outside of the dress neckline.
When Stan locks the door to show Peggy his "relaxation technique" before the Playtex pitch, he is wearing a wedding ring - even though Stan isn't married. When he stands in front of her, the wedding ring is gone.