At first, Mike Road provides the voice for the submarine Navigator while Henry Corden provides the voice for the submarine Crewman, but sixteen minutes into the story they're switched; now Henry Corden provides the voice for the submarine Navigator while Mike Road provides the voice for the submarine Crewman.
Jonny sees a periscope behind the Quests' boat. It submerges as he turns to tell his dad about it. While he's telling Dr. Quest about it, the periscope submerges again. It should not have submerged the first time.
As a parting gift, Prof. Ericson gives Jonny the missing gargoyle statue. He carries it and lifts it into the car like it was ceramic (hollow) and not like the hefty, solid, stone item that no single ordinary man can lift.
Dietrich's first burglary is in the daytime, and Gunnar tells the Quest team that it happened "this afternoon." However, there was an intervening scene of Dietrich and Ivar meeting in a graveyard at night, so Gunnar should have said "yesterday afternoon."
Hadji's fond memory of the "water lily girl ghost" is at odds with his consistently negative opinion on female companionship, both before and after this episode.