After Odo puts an intoxicated Kor in a holding cell he walks into his office, as he sits at his desk the door leading from his office to the promenade is open. Yet a second later Odo is surprised by Koloth's sudden appearance and asks him how he got into his office, the door being wide open is an obvious explanation.
When Dax returns to DS9 and goes to Ops, Sisko is seen on the other side of the area, looking toward her. When the camera angle changes, Sisko is slightly turned away, then turns toward Dax as if just noticing her.
No death yell to warn Stovokor that a Klingon warrior is arriving.
This episode features Koloth, Kang, and Kor, who all appeared as "new" Klingons (the ones seen since Star Trek: The Motion Picture). However, since they were recurring characters from the original series, they should have appeared as "old" Klingons (who appeared so much like humans that they actually passed for humans, such as in The Trouble With Tribbles).
Before going into battle, the Klingons (plus Dax) sharpen their blades. Closeups of their Bat'leths reveal that the edges are blunted and the tips rounded.
When Odo is standing outside Kor's holding cell, the camera pans up and the Velcro patch holding Odo's combadge to his uniform is visible.
Koloth pokes the lookout on the shoulder yet the man rubs his neck.
Kor, Kang and Koloth not appearing as they did in Star Trek (1966) is explained in season four of Star Trek: Enterprise (2001).
Kang was somehow able to track Dax to Deep Space Nine while remaining unaware that the symbiont had been passed from Curzon to Jadzia. There is no sensible way to have found her current location and assignment without also discovering that she was a young, female Starfleet lieutenant and not a 100+ year old male Federation ambassador.
Kang reveals that he agreed to meet 40 of the Albino's best men in "honorable" combat." Sending a force that outnumbers your enemy 10:1 is not honorable.