When Raymond goes to the front door to tell the twins to stop playing on the lawn, you can see their shadows on the porch and one fairy wing through the door as they wait for their cue to come inside.
When Frank exits the house in the last scene before the tag, his shadow on the door is immediately followed by the shadow of some equipment.
A running gag throughout the show's run is that Robert has to touch food to his chin before eating it. In the opening scene, he's eating potato chips and at one point puts them directly into his mouth.