Metallica: Music For Monkeys?
The main thrust of the study was to determine if primates are capable of emotionally responding to music as people do. And the findings state that music "inspired by the soothing calls of contented monkeys relaxes the animals when it is played back to them."
So where does Metallica come in? The study took 30-second excerpts of human music like Samuel Barber, Tool and Nine Inch Nails, and the tamarin monkeys had no emotional response -- until they were played 'Of Wolf and Man.' The scientists theorize that the rising and falling tones are reminiscent of the monkeys' call, and that is what they relate to in the clip.