Continuity mistake: Doug finishes playing the tennis game on the TV with Arthur and goes into the kitchen to get the Cheese Doodles. While talking to Carrie, he puts the Cheese Doodle package on the table with a can of cola behind it. He then goes to get a glass from the cupboard and in the next shot you see the cola is in front of the Cheese Doodles.
Plot hole: In this episode Arthur scams Deacon and several other parents for phony piano lessons because he doesn't actually know how to play the piano. However, earlier in the series (Art House episode, S1 - E24) we learn that Arthur can play the piano when he temporarily moves out and after his house warming party Doug says to Carrie, "Who knew Arthur could play the piano like that?"
Revealing mistake: In the final scene of the episode, Arthur is searching for used bottles of nasal spray. He empties the contents of the trash can on the kitchen floor and finds one after sifting through the trash. However, the bottle had already been positioned on the floor next to the trash can before he picked up the trash can so it would be easy to find when the trash was emptied on the floor.