Scientists conducted a study on 14 tamarin monkeys in which they were played a variety of human and "monkey" music to see if the songs had any effect on their mood. The monkeys were mainly unresponsive to human music, but the "monkey" music-"tunes that incorporated features commonly heard in monkey calls, such as rising and falling tones"-did provoke a response: They were soothed by calming monkey sounds and agitated by stressful monkey sounds. And human music?

The animals were played Samuel Barber's Adagio for Strings and a soft piano piece from The Fragile by rock band Nine Inch Nails, followed by Metallica's Of Wolf and Man and an excerpt from The Grudge by rock band Tool.

They then heard the specially composed monkey music.

The only human music that elicited any response was the heavy metal band Metallica, whose music had the unexpected effect of calming the monkeys.

You can hear the "monkey music" at the link above. You can hear Metallica pretty much anywhere on the Internet, but keep quiet about it because those guys are pretty litigious.