When Perry is in the apartments to replace the doorbells, he stands on a chair and places a new door buzzer and a screwdriver on the top of the door frame to the right of the existing doorbell. Cut to a tight shot of Perry, and the doorbell and the new door buzzer are to the left of the existing doorbell.
At the end of the show, Karl Reynolds asks Rhoda to consent to an annulment of their marriage, but earlier in the show Perry commented that their marriage wasn't legal since she was still married to her first husband.
(at around 25 mins) When Perry enters his office as Della and Paul are reading the newspaper, it can seen that that the newspaper is a prop; the front page has writing, but the inside pages are blank.
At one point in the courtroom during questioning about the doorbell, the judge addresses Perry as Mr. Burr.