Monkeys' "Do Not Disturb" Sign?
Scientists aren't sure exactly what it means, but the rough translation might be "leave me alone."
The mandrills will cover their eyes for more than 30 minutes.
According to the study, "the gesture might have a locally respected meaning," possibly to "inhibit interruptions as a 'do not disturb' sign operates."
Because the gesture emerged naturally, independent of human involvement, and has now lasted a full generation, it could be considered a cultural behavior, the authors say.
Photos courtesy Mark Laidre, University of California, Berkeley