Can I Keep Him...Please

My daughter brought home a stray rat the other day. No joke. How do I know it was a stray and not just...well..a rat. I called the vet, and apparently only domestic rats are black & white. So the rat Cheyenne scooped up with a paper cup was a stray, or lost, or abandoned pet rat. Black plague..black schmague, you know what I mean. Thankfully the rat died that night, and Cheyenne is still alive a week later.