The man-eating lions of Tsavo, that pair of legendary beasts who killed about 35 railroad builders in Kenya in 1898, have long been attached to one question: What caused them to turn to humans? More than a century later, researchers were able to use remains kept at Chicago's Field Museum to arrive at an answer—or two. Bruce Patterson and Larisa DeSantis created dental molds and then casts of the lions' teeth, with those casts then subjected to tests designed to surface any microscopic wear. One prevailing theory was that the cats were so hungry due to a lack of prey they had to resort to eating men. Except the tooth damage you'd expect from crunching bones—consuming whole carcasses, not just fresh meat, would be natural in times of extreme hunger—just weren't there, per the study, published in Scientific Reports.
Quite the contrary, their microwear was "similar to what you'd see in a zoo lion," says DeSantis. But the teeth did give up a secret. The lion identified in a prior study as having eaten the most humans (likely 24) had lost three lower right incisors and suffered from a canine-tooth root-tip abscess, which would have severely impaired its hunting ability. "Humans are so much easier to catch," says Patterson. A press release explains the teeth of the second lion, believed to have eaten 11 humans, were in better shape. A second press release notes that we can only speculate about why the human bones weren't consumed: It may not have been feasible because of the dental disease, or the remains may have been recovered by survivors before the lions had finished. Regardless, the researchers say dental disease was probably a big factor. (Here's how a python can swallow a man whole.)