Revealing mistake: At the end of this episode when Carrie is walking away from Mr. Big's apartment; she notices an Autumn leaf, and follows it with her eyes as it floats down to the ground. However, this leaf is actually digital and not real. Sarah Jessica Parker had to pretend to be staring at a leaf that wasn't there while filming; and if you watch her gaze carefully, it doesn't always follow the path of the leaf. She looks down too soon, before the leaf has a chance to float down that far.
Revealing mistake: Just after Big has left NY for good, Carrie leaves his apartment and is walking down the street. A leaf (that another mistake pointed out was digital as it was falling to the ground) is lying on the sidewalk. Carrie picks it up, but it is obviously an artificial one made from plastic and fabric.
Continuity mistake: When the horse drawn buggy is pulling over to the curb in front of the hospital, you can see it dodging traffic and cars. But after Carrie leaves and the buggy pulls away with only Mr. Big, suddenly there are no cars or traffic in sight. The entire street from that direction appears to be completely empty.
Visible crew/equipment: When Carrie arrives at the hospital room, Miranda is walking back and forth trying to break her water. When she turns back towards Carrie, you can see something sticking out prominently from under her hospital gown on the right side of her abdomen. The object appears to be swinging around on a line or wire as Miranda moves. When Miranda gets closer to Carrie and finally stops just in front of her; you can see the entire wire or line attached to the object slanting diagonally from her left shoulder, across her chest and down her abdomen, just right of the center. The protruding object, and line or wire must be her mic.