When Carla holds up the Polaroid picture being auctioned, it is black on both sides - there is no image on it.
At approximately fourteen minutes in during the basketball game McHale makes a shot then gets the ball and runs to the adjacent wall and there is another backboard and basket. This second shot he makes is on a wall 90degrees from the previous one.
Cliff states that basketball was invented by the ancient "celtics". They were called Celts, not Celtics. Plus the C should be pronounced as an S, not as a C. The mispronunciation of the team name goes back to the team's founding in 1946 in which a poorly educated fan base and ownership showed pride in the city's Irish heritage but were distant enough from the original culture that they did not know how to pronounce the name of their own race.