After hitting her over the head & knocking her out, Peggy drags an unconscious Jennifer into a small room/utility closet containing a water heater. Peggy decides to kill Jennifer by gas poisoning. At approximately 38:50, right before Peggy puts out the pilot light on the water heater you can clearly see that the door to the little room is open. As she kneels down to blow out the pilot light, the door is shown closed. When she stands back up again to leave, the door is open again.
The scene on the rooftop with Jonathan, Jennifer and Peggy must have taken several hours to film. When the three first get to the roof, the natural lighting indicates mid-day, by the end of the scene, the sun is setting, natural lighting is darker.
Peggy and Tony interact while she's at his ticket office. But that evening, when she has him try shrimp at the office party, he doesn't recognize her voice.