Growing up, most children are taught that it’s rude to whisper. But this etiquette rule is something clearly not passed down the generations in cotton-top tamarins. The first non-human primate to whisper, this behaviour was first discovered at New York City’s Central Park Zoo.
The keepers were originally carrying out an experiment into alarm calls and how the monkeys warn each other of danger, but instead they were greeted with silence. When going through the recordings, they later discovered the monkeys were communicating after all, but in very hushed tones. They realised that when a distrusted keeper walks in, the monkeys began to whisper.