The lions at the Copenhagen Zoo eat the remains of a healthy young giraffe named Marius in February. It's unclear whether the lion pictured was one of those euthanized. Kasper Palsnov/AFP/Getty Images hide caption

itoggle caption Kasper Palsnov/AFP/Getty Images

A security guard closes the gate at the Pittsburgh Zoo, where a 2-year-old boy was killed Sunday. John Heller/AP hide caption

itoggle caption John Heller/AP