When George plays the Bubble Boy in Trivial Pursuit, the Bubble Boy moves his piece to a place on the rim of the wheel on the board and announces, "For the game." In Trivial Pursuit one wins by moving to the /center/ of the board and answering a question, not the rim.
On the drive up to the cabin, the back seat of the car is full. You cannot see out the back window. After leaving the Bubble Boy's house, fire trucks pass the cars. The shot of Jerry and Elaine in the car shows the back seat empty and the light of the firetruck visible behind them.