Other mistake: The same dungeon set is used several times throughout the series, just furnished differently.
Revealing mistake: Any time a laser is fired in the show, there are no scorch marks on the walls where they hit.
Get Smart (1965)
2 mistakes in show generally
Starring: Barbara Feldon, Don Adams, Edward Platt, Robert Karvelas
School Days - S1-E3
Max: When the moon is full, the tide is high.
Old Lady: You must want the spy school, that's next door.
More trivia for Get Smart