Open the Door Witchcraft - S1-E28
Deliberate mistake: Sam and Darrin are "trapped" in the garage; however, you can see a side door.
City of Fire - S1-E3
Deliberate mistake: When one of the yellow fire trucks moves away from the burning Thompson Tower, the back of the truck is set alight by the flames.
Deliberate mistake: "Long Live the King": The Seaview's 8 huge picture windows were a concession to design over practicality. Though they knew that such big windows could never withstand deep sea pressures, the producers wanted the characters - and the audience - to be able to see all the underwater wonders "up close." The "impossible" windows became one of the show's most popular features. (00:25:10)
The Pieces of Fate Affair - S3-E23
Deliberate mistake: Because lawyers for real-life review columnist Judith Merrill were not amused by the parody of her and sued, the name Judith Merle is very obviously dubbed over throughout the episode (and changed in the credits) to Jody Moore. (00:32:50)