score:4
Those studying and commenting on Tobit have long been intrigued and puzzled by the presence of Tobit's "canine companion". This answer is based on Carey Moore's work, Tobit: A New Translation with Introduction and Commentary (Anchor Bible 40; Doubleday, 1996). He signals the measure of bemus*m*nt this creature brings as he begins his comment on the 11:4 occurrence (p. 261):
That elusive dog again!
He offers most of his discussion about this canine character at 6:2 (pp. 197-8). Condensing and simplifying, with a few notes of my own, the main options canvassed by scholars are these:
Important to note for OP's form of the question, though, is that the dog has no particular relationship with the archangel Raphael, but appears to be part of the Tobit household (or perhaps a friendly "neighbourhood" dog): the two explicit mentions of the dog marking the beginning (6:2) and end (11:4) of the journey.