As in other Star Trek series, little inside jokes that are not often shown on camera appear on the set. For example, the Jupiter Mining Corporation from the BBC comedy series "Red Dwarf" has an office on the Promenade. See more...
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Star Trek: Deep Space Nine (1993) - 29 mistakes in entire show
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.