Many mammals, including dogs, rats and cats, sniff each other out when they meet. For rodents at least, sniffing intensity signals social status.
Subordinates stifle sniffing in the face of a dominant rodent, or risk its wrath. Snuffing sniffing is an appeasement signal.
Such sniffing has nothing to do with smell. Instead, the behavior itself signals subordination.
Biologist Daniel Wesson observed: “This sniffing behavior might reflect a common mechanism of communication behavior across many types of animals and in a variety of social contexts. It is highly likely that our pets use similar communication strategies in front of our eyes each day, but because we do not use this ourselves, it isn’t recognizable as ‘communication’.”
Sources:
Daniel W. Wesson, “Sniffing behavior communicates social hierarchy,” Current Biology (7 March 2013).
“Sniff, sniff: new form of animal communication discovered,” ScienceDaily (7 March 2013).