At the fancy dress party for the new crew, Margaret Ursula and Hero are seen in the room upstairs talking. As Don is seen going upstairs towards the room you can see Ursula dancing at the foot of the stairs. When he reaches the room he hears them talking and the door opens. He runs away. Ursula comes out of the room with Margaret and Hero, but only seconds ago Ursula was downstairs and she had not come up whilst Don was there.
When Don arrives at the party you can see he has not drawn on any black eyebrows yet later you see him with black eyebrows drawn high on his forehead. This happens continuously throughout the party scene