Killer monkeys are one of the best subgenres of horror. More often than not, a primate going mad is simply nature correcting itself. The premise usually follows a diabolical scientist or some researcher performing unethical experiments or procedures on a monkey for the sake of science and the greater good. They usually fail to anticipate the monkeys’ reactionary behaviors from being injected with an unwanted hormone, for example, and unwittingly trigger a much-deserved murderous rampage. It’s a perfect example of “they had it coming” if you’ve ever seen one.