During a voiceover George says "Is it sch-mutz or sch-mootz?" in reference to pronouncing the word "schmutz". In fact, actress Ellen Muth was asking the voiceover producer how to say the word, and the director decided to leave it in the dialog.
A scene with a group of Metermaids (featuring secondary character "Roxy") is a direct spoof of the opening Roll Call scenes from Hill Street Blues (1981), down to the style of camera work, a balding cop running the meeting (finishing it with Hill Street Blues' Character Phil Esterhaus's signature line "be careful out there"), and finishing with the meter maid mini-trucks leaving the station and the squad cars from Hill Street Blues (while the Hill Street Blues theme plays in the background).
The title "Send in the Clown" is a reference to the song "Send in the Clowns" by musical composer Stephen Sondheim. In addition one of the reaps is a character whose last name is Sondheim. Mandy Patinkin, who plays Rube, is a noted interpreter of the musical works of Stephen Sondheim and is known for his work in musical theater, originating iconic roles such as Georges Seurat in the Sondheim musical 'Sunday in the Park with George.' He recorded "Send in the Clowns" on his album 'Mandy Patinkin Sings Sondheim.'
Joy and Clancy in the car in the parking lot after therapy. At the start of the scene the camera moves in toward the Lass car, the footage is run double fast. At the end of the scene the camera pulls away from the Lass car at normal speed. Both approach and withdrawal are the same footage. They filmed with the camera pulling away for the closing shot, then decided to reverse the footage (and speed it up to hide the reversal) for the opening approach.