Monkeys have been found to be fans of heavy metal music after scientists in America found it calmed them down.
When a group of cottontop tamarins were played a variety of tunes, from classical to jazz, only songs by thrash metal outfit Metallica made them react.
But rather than making them agitated or aggressive, the heavy tracks had a soothing effect, Psychology Professor Charles Snowdon, of the University of Wisconsin-Madison, found.
Dr Snowdon, who teamed up with National Symphony Orchestra cellist David Teie, also played the monkeys tunes composed specifically for them.
Although they enjoyed Metallica, they were much more interested in these pieces.
A melody based on the short calls of scared monkeys led to anxiety levels soaring, while one based on long calls the creatures make when they are happy had a calming effect.
The pair also found monkeys use tone and pitch to express emotions.
Dr Snowdon told the Royal Society Journal Biology Letters: "My talking does not necessarily tell you about my emotional state.
"When I add extra elements, change the tone of voice, the rhythm, pitch or speed, that is where the emotional content is contained.
"Monkeys interpret rising and falling tones differently than humans. Oddly, their only response to several samples of human music was a calming response to the heavy-metal band Metallica."
He said human babies are also able to interpret tone and pitch.
"We use legato - long tones - with babies to calm them. We use staccato to order them to stop," he said.
"Approval has a rising tone, and soothing has a decreasing tone. We add musical features to speech so it will influence the affective state of a baby. If you bark out 'PLAY WITH IT' a baby will freeze."
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