In this episode, when Black investigates several killings by a pack of savage dogs, he discovers a strange old man who teaches him more than he ever knew about the Group.
Guest star Armstrong would reprise his role later in the season, while Stone was the casting director for both Millennium and its sister show The X-Files.
"Beware of the Dog" received mixed reviews from television critics, and was viewed by approximately 6.37 million households during its original broadcast.
They stop near a small town to read their map, but a pack of dogs break into their van and maul them to death.
The locals believe he is unconscious and discuss the "situation"; however, Black is awake and overhears everything, realizing there is a greater threat at hand.
"Beware of the Dog" was written by frequent collaborators Glen Morgan and James Wong, and directed by Allen Coulter.
[5] "Beware of the Dog" features the first appearance by R. G. Armstrong as The Old Man, a recurring character who would reappear in the two-part episodes "Owls" and "Roosters".
Darin's music has been noted by Millennium's resident composer Mark Snow as a hallmark of the works of Morgan and Wong.
"Beware of the Dog" marked the pair's first use of the singer in Millennium, but his music would later feature in the episodes "Sense and Antisense", "Monster" and "Goodbye Charlie".
[12] Bill Gibron, writing for DVD Talk, rated the episode 3.5 out of 5, noting that its "atmospheric elements do not quite add up to a cohesive whole".
[13] Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files, Millennium & The Lone Gunmen, awarded "Beware of the Dog" one-and-a-half stars out of five.
[10] Writing for the Star Tribune, Bill Ward felt that the episode featured a "lighter" tone than usual, comparing it to The X-Files.