4 Rms Ocn Vu - S3-E8
Factual error: Some of the visitors came to the Keaton "hotel" (their house) for the "ocean view." This takes place in central Ohio (near Columbus). There are no oceans around there.
Factual error: The forces of Cassiopeia all sport the crown-like "W" sign which is the shape of that constellation... but only as seen from earth! These five points in three-dimensional space (like all star signs named after anything) look like that when viewed from our own planet; but from anywhere else, they aren't shaped like that at all. Why would they chose to see themselves through a very specific angle of view from some other distant planet (earth)?
Factual error: There is an intercom system in the library that is used by Derek (and at the end, Edward). They try pushing down the buttons to talk (which is normal for intercoms), but then each time, we are hearing Ricky and his grandfather's conversation from inside the car that's outside without using the intercom connected to the house. In the 80s, a house intercom system would not pick up a conversation in a parked car outside.