At the beginning of the episode, the Immortal Paul Karros racks the slide on a nickle plated Desert Eagle, which causes the slide to lock back. This indicates the magazine is empty. He then manually drops the slide, and holsters the pistol. It now has an empty chamber and an empty magazine. A few seconds later it has a round chambered, and ready for use.
Even though the opponent is facing Mac when he loses, a moment after the beheading, his body falls to the knees, then over, away from Mac as if it was facing the other way.
When Karros kills the assassin with his sword, being mortal, there should have been blood on the blade, but in the follow-through swing, the blade is clean.
The North American episodes of this series are set in the fictional city of Seacouver, Washington, USA. However, the city skyline shown a few times in this episode (e.g. at about 0:20:00) is clearly that of Vancouver, BC, Canada, where it was actually filmed.
This episode was probably planned to have had the same opening credits as the previous two episodes but an early change left Philip Akin going uncredited and Lisa Howard being credited twice (in the opening credits and then as a guest star moments later).
When the coroner shows Duncan the body of the assassin, he says he was sliced like a tomato. The the coroner is British, he should have pronounced it the English way (toe-mar-toe), not the American way (toe-may-toe)