Although rare, there are stories of street rat domestication, but these rats, she said, have a much harder time finding a home. Street rats, she explained, are brown rats, which are said to be less civil and healthy, and are different from “fancy” rats, the species that most New Yorkers look to adopt.

Ms. Stewart was first introduced to the idea of pet rats eight years ago at a studio party in Williamsburg, Brooklyn, where someone told her that a rat named Minky was up for adoption. Ms. Stewart, a native New Yorker who had owned a hedgehog in college, was interested.

“As soon as I got her, I was so amazed by how incredibly cool, smart and sociable they are,” she said. “They don’t bite. They’re like little dogs, mixed with a cat.”

That was five rats ago.

Now, Ms. Stewart is a full-fledged adoption advocate, who often finds herself explaining rat culture to co-workers. “Their initial reaction is just kind of like, ‘Really?’” she said. But she added that after an elevator pitch and a few photos, most become receptive to the idea.

The only downside, she argued, is their life span, which on average lasts barely more than two years. This can mean heartbreak, more often.

In the rat-adoption community, there is a term for a favorite rat — a “heart rat,” which Ms. Stewart considers to be her fallen furry companion, Markey. “That’s the hardest part of having a rat,” she said. “When they pass away, you’ve created these bonds with them.”