Gordon Burghardt kept a lion cub named Meg in his home at the behest of the Knoxville Zoo. To help Meg get out some energy, Burghardt and his wife would often play with Meg in their wooded, unfenced backyard. One day, a neighbor’s dog appeared, tail wagging. As an ethologist—a scientist who studies animal behavior— Burghardt could see that the dog was giving clear signals that he wanted to play, not fight, but would the lion cub be able to read them? After all, these are two creatures separated by around 45 million years of evolution.