Ellen Heber-Katz, a scientist at The Wistar Institute in Philadelphia, used to study autoimmunity–that was until she noticed something strange in the mice she was using to model lupus: The small holes that she had poked in their ears to distinguish the animals from one another kept closing. At first she thought her postdoc, Lise Clark, had forgotten to make the holes in the first place. But Clark clearly remembered doing it. Together, Heber-Katz and Clark pierced new holes. Within days, they closed, too. “Every day they got smaller and smaller and then just disappeared,” Heber-Katz says. And, there was no scar–the tissue was perfect. They wondered: “If we could find out what it was that was creating this response, we could treat wounds that way!”