Diamond Jack - S7-E3
Revealing mistake: As Terri exits Jack's bedroom to stall the diamond thieves, you can momentarily see into the girls' bedroom. The wall that should be between the girls' bedroom and Jack's bedroom is missing and the floor and blue curtains of Jack's bedroom set are visible. Someone's arm wearing a light colored shirt (John Ritter's sleeve is brown and Joyce DeWitt's sleeve is black) can also be seen moving. (00:25:00)
Diamond Jack - S7-E3
Character mistake: At the roller skating rink, Jack looks at the menu on the wall in the snack bar while ordering two sodas and says "What are they... 50 cents a piece?" However, only food items and candy are listed on the menu and drinks are not mentioned at all. How did he know the price?
Answer: I believe you are referring to the artwork of Alphonse Mucha. On the wall next to the front door was "Feather" (which is one half of "Primrose and Feather"). Above the telephone in early episodes was "Zodiac". Also seen through The Apartment was "Spring" and "Autumn".