Chimpanzees are omnivores and not just in the sense of eating grubs or enjoying a little meat when they can scavenge it. They kill. In fact, some troops will go hunting without any visible prey nearby — which is a pretty interesting bit of thinking and planning, in and of itself. Disturbingly, what they hunt is other primates. In this video, a group of male chimps hunt and kill some colobus monkeys, a scene that narrator Sir David Attenborough described as “most distressing/upsetting moment” in his career during a recent Reddit AMA.