Add Yahoo as a preferred source to see more of our stories on Google. When you buy through links on our articles, Future and its syndication partners may earn a commission. In a bizarre yet intriguing ...

Claudio Mello was conducting research in Brazil’s Atlantic Forest about 20 years ago when he heard a curious sound. It was high-pitched and reedy, like a pin scratching metal. A cricket? A tree frog?

Part 1. 'I don't do calls' -- Crossing the sound barrier -- Tone and timpre -- Pitch and frequency -- Rhythm and timing -- Part 2. Put it all together and what have you got? -- Simple calls -- Simple ...