Unsurprisingly, its Chimpanzees. I’ve once read about a case where researchers studied a certain group of chimps, and observed that from time to time a young would disappear from the group, never to be seen again. Turns out an older female was luring them away from the group and murdered them. Apparently, there is a non-interference rule in wildlife research, so this went on until the group simply died out, because every single young fell victim to the serial killer.

Yeah, everybody is making jokes about cooking with blood in this thread, but they’re really just describing German cuisine. I remember eating blood gruel with potatoes and spinach as a kid. Tastes awful.