Deliberate mistake: The dying Vantika hides his consciousness away in a portion of Dr. Bashir's mind. At one point, "Bashir" (heavily cloaked in clothing and shadows) comes up behind Quark and makes sure his demands are clear. At this point, it should still be unclear just how Vantika is still "alive", and whose body he is using. However, when he shoves Quark away, for a fraction of a second, Bashir's face can be seen under his hood. They were true to plot in using the right actor (though he shouldn't have been seen), it is possible some might have spied the secret earlier than the show meant to reveal it.
Broken Link - S4-E26
Revealing mistake: During the fight between Garak and Worf near the end of the episode, a Jefferies tube door is knocked out of its frame to reveal the end of the set - a dark room with a wooden scaffold and various other pieces of equipment (slow-mo helpful but not required). (00:36:00)
The Way of the Warrior (1) - S4-E1
Julian Bashir: They broke seven of your transverse ribs and fractured your clavicle!
Elim Garak: Ah, but I got off several cutting remarks which no doubt did serious damage to their egos.
More trivia for Star Trek: Deep Space Nine
The Way of the Warrior (2) - S4-E2
Question: What does Dax say to Worf when she first meets him? Where it loses something in the translation.
Answer: Worf: Curzon's name is an honored one among my people. Dax: (in Klingon) Yeah, but I'm a lot better looking than he was.
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