It sounds like a witches' recipe: gather the hearts of a fence lizard; a little brown bat; a naked-tailed armadillo; and dozens of others. "So initially we tried to get them from zoos, but unfortunately that didn't work out very well. We couldn't get any samples, even when the animal died, we couldn't get a heart." Guo Huang, a developmental biologist at the University of California, San Francisco. He says they had more success obtaining specimens from the jars of natural history museums.