There is a vent that is visible on the wall between the hallway and the office, directly above one of the picture frames. The vent is important to the plot of the episode. It does not appear in any other episodes of the series.
At the very end, just before the collapse of the glasses rack above the bar, many glasses can be seen moving above Rebecca as she speaks to Sam and the alcohol agents.
During a scene in the pool room, where the guys are playing cards, you can see the main room from in front of the set. The guys have put up a blanket over the main entrance to keep the cigar smoke from filtering out. The camera is at an angle looking out of the pool room towards the covered entrance. To the left of the blanket, you see wall, then the main room.