Plot hole: Solo blows open the ceiling vent of Illya and Marion's cell, and she stands on Illya's shoulders until Solo can reach her and pull her out. This leaves Illya with nothing/no one to stand on, no way to reach the vent and no apparent way out of the cell. But he's out just the same in the next scene, with no explanation as to how. (00:42:40)
Continuity mistake: In Waverly's office, Illya hones his combat skills by swinging at a suspended wooden block with a baseball bat. When the alarm goes off, Illya puts the bat down on the table, and he and Solo rush to the computer console. In the next, reverse angle shot, the block is still hanging from the ceiling, but the baseball bat has vanished from the table.
Other mistake: Vladik, incorrectly, tells Donfield on the phone to stand at the hot dog stand at 3 pm Monday. It should have been 11 am. Donfield in the "meet" scene refers to his 11 o'clock feeding" and Mr. Smith tells Solo (Donfield) his next meeting is between one and two pm. This would be impossible if the original meet was at 3 pm.
Revealing mistake: Every time the villains' deadly gas, "hydro," is mentioned, the word is badly and very obviously dubbed in, and doesn't match what the actors' lips are saying. This occurred because the original name used, "freon," turned out to be an existing (and patented) refrigerant gas, so the name had to be changed to avoid a trademark lawsuit. (00:28:45)
Revealing mistake: When Napoleon Solo arrives at the train station, both the name of the newspaper the man in black is holding, and the name on the station sign are backwards. Additionally, as he arrives by train the man in black is on the left side of the shot. After exiting the train, the man in black appears from the right side of the shot. (00:12:35)
Continuity mistake: As Napoleon Solo arrives by train, he passes two donkey drawn carts and approaches a woman whose sweater collar is overlapped from right to left. In the next shot, showing Solo exit the train, the donkey carts are now to the right and the woman's collar is now overlapped left to right. (00:12:35)
Other mistake: In the last scene of the episode, the opening shot is a Boeing 707 in flight. The 707 logo on the tail is backwards. It appears they flipped over a piece of film stock from a shot earlier in the episode, where the same plane was flying in the opposite direction.