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)
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)
Continuity mistake: When Solo begins trying to seduce the dancing girl with the line, "We shall taste paradise," he's standing at least a foot away from her. But in the very next shot, they're suddenly in a clinch: her hands are on his cheeks and they're about to kiss. (00:29:15)
Plot hole: The typewriter case containing the secret plans is said to be boobytrapped with nitroglycerine. If dropped, says the Thrush agent, it "could blow us all up." Yet it survives a plane crash intact and is later wielded as a club several times in the cavern fight scene, and somehow it never explodes. (00:43:05)
Continuity mistake: In Waverly's office at the beginning, the contemplative Illya's hand is draped over his glasses salute-fashion in wide shot. But in close-up, it's suddenly curled into a fist at the side of his head. Next shot, he's "saluting" again. (00:06:50)
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.