Muttville Senior Dog Rescue uses a resident cat named Mustache to run live cat-compatibility assessments on adoptable senior dogs — a supervised meet-and-greet that determines whether a dog can go home to a multi-pet household.

Walk into Muttville Senior Dog Rescue on Florida Street on any open day and you will find, among the senior dogs, one cat. His name is Mustache, and if a dog is being considered for a home that already has a feline resident, Mustache is the one who decides.

The organization, at 750 Florida Street in the Mission, describes itself as the country's first cage-free senior dog rescue — founded in 2007, currently open Tuesday through Sunday, 11am to 4pm. It runs what the staff calls a cat-compatibility assessment, the subject of a Forbes piece published Wednesday by journalist Jen Reeder. The mechanics are modest: Mustache holds his position in the room while a dog, under supervision, is allowed to react however it wants to react. What happens in those minutes tells Muttville something an intake form cannot. Total indifference to the cat, cautious curiosity from a safe distance, or plain friendliness — those are passing marks. Barking or aggression means the dog gets flagged as a better fit for a cat-free home. Mustache enforces his own version of acceptable behavior: dogs that move in too fast for a sniff have reportedly received a corrective swat.

The logic behind it is blunt: a dog's history with cats, and its live behavior in Mustache's company, is the strongest available predictor of how it will do in a home that has one. A form asks the previous owner; Mustache asks the dog.

Muttville has been operating on Florida Street under the founding model of Sherri Franklin, who opened the shelter in 2007 and retired earlier this year. Laurie Routhier, the organization's chief operating officer for more than a decade, moved up to CEO. In that span, Muttville has placed more than 14,190 senior dogs; it also runs a seniors-for-seniors adoption program and hospice placements at no cost to adopters. Standard adoption fee is $250.

The Forbes profile runs the same week Muttville opened what it calls a permanent new headquarters on Florida Street — a "colorful, comfortable paradise," per the shelter's own description, a significant step for an operation that spent years in temporary and improvised space.

Stop in on a Tuesday and you might see the evaluation happen: a senior dog trying to make its case, and a cat deciding whether to give it one.