The clinic, in a town called Puerto Peñasco, is operated by Compassion Without Borders (CWOB), a U.S. nonprofit that provides free and low-cost veterinary care.
A kind-hearted local woman brought him in to be neutered, and after he recovered, he was taken back to town.
But the very next day, a familiar figure brightened the clinic's doorway. It was the dog with no name.
"He's very, very friendly," Christi Camblor, executive director of CWOB, tells The Dodo. "His tail never stops wagging. He's just incredibly affectionate and outgoing."
Did we mention intelligent?
After all, he knew exactly which door to knock on.