Some think the healing experienced by immortals is inconsistent. Duncan and Connor both experience complete healing while the Kurgan carries the scar across his neck and throat where Ramirez failed to cut through far enough to sever his head. The scar could then be theorized to be a result of the fact that the neck is the one part of the body to demonstrate long term damage due to it being an immortals Achilles Heel. As well, it has been demonstrated multiple times, that an immortal can be affected by alcohol and drugs.
This episode is a variation of a theme in the series. What happens when mortals learn of immortality. In this case, mortal Dr. Paul Wilder is experimenting on Duncan to find a way to replicate his healing factor.
When Duncan calls Tessa from the phone booth after he leaves the receiver hanging you can see the Pay Phone Number it's 722-9536
The episode features no flashback scenes. "Highlander" episodes typically feature flashback scenes, depicting the past of one or more characters and drawing a connection to the present.