In what is thought to be a world first, monkeys at Colchester Zoo have developed their own sign language.
The Mandrills put their hands over their eyes when they want to be left alone, a gesture never seen anywhere else.
At first zoo keepers thought there was something wrong with the monkeys eyes, but after studying them for a while scientists worked out they were creating their own 'do not disturb' sign.
It is the first time monkeys have taught themselves their own gestures.
Other monkeys have also been taught to open their mouths on command so zoo keepers can check their teeth.