When Molly is showing her friends her bridesmaids dress, her cell phone is on the near side of the ottoman, but when the scene shifts and her cell phone rings, it has moved to the far side of the ottoman.
When Molly's boyfriend is honking his horn and waiting for her early in the movie there is a reflection in his car window of someone walking by on the sidewalk, but when the camera angle shifts there is no one there.
When Molly is talking with her three friends early in the movie while wearing the bridesmaids dress, the girl in the red shirt sits down and crosses her legs. When the camera next focuses on her, her legs are uncrossed, then they're crossed again in the next camera shift.