None of the air vent covers that the spider goes through have any screws in them holding them to the wall, as all vent covers normally have.
Each time there is a scene in the air ducts, the distinctive pattern of stains on the end panel are identical no matter which section of the system they are viewing. The set for the air ducts was obviously very limited with only one long section that was used multiple times.
While supposed to be set in New York City, the Australian set comes through, doorknobs are about 3 ft from the ground in the U.S., here the knobs are halfway up the doors.