Other mistake: When playing poker, Stef says she has all hearts which is a flush. However if you look at the cards she puts on the table, there is a 6 of diamonds and 3 of clubs. Therefore, not a flush. Everyone at the table, (Lou, Mr. Prezants, Deacon, Spencer and Doug) all agree it's a flush. (00:13:30)
Other mistake: When Doug is drawing a picture to explain to the nurse why he is there, a man purchases a beverage from the "Hot Drinks" machine behind Doug. The drink is ready unrealistically fast and the man immediately takes a sip from an obviously empty cup. Those machines produce notoriously hot beverages, so if the machine actually worked the man would have scalded himself.
Other mistake: When Doug is saying that Arthur does nothing that Deacon just listed, there is a camera angle of him walking down the aisle with Deacon. In this camera angle only there is a blip to the top right of the screen. This little black mark stays in shot while the camera is moving and is only in this one angle. In other shots of the same angle the black mark is not present. Clearly something was on the camera lens during filming. (00:05:30)
Other mistake: When Doug and Carrie go to visit the new neighbour, Jessica, Carrie tells her that they live at #8013; however many other episodes we see the numbers 3121 on the Heffernan's door and later learn that the Heffernan's live at 3121 Aberdeen Street in Rego Park. (00:28:35 - 00:29:35)
Other mistake: When Doug sits down to eat and Arthur touches his food, Doug says, "That's what my sandwich was missing, a finger with a loose bandaid on it," and pushes Arthur's hand away. When he does this you can see Arthur isn't wearing any bandaids on his hands. (00:00:05 - 00:01:00)