If an orangutan blows a raspberry, smacks you on the side of your body or gives you a nip on the arm, don't worry.
He's simply asking if you want to play, it seems.
For the great apes communicate intelligently using an unspoken vocabulary of gestures, movements and smacks, scientists say.
Forty frequently used body language signals were identified by British researchers who spent nine months observing orangutans in three European zoos.
The results have been compiled into the first ape dictionary - a guide on how our cousins chat to each other in the wild.
It shows the apes have at least 25 signals or gestures for "I want to play", for example - ranging from a back roll and somersault, to a yank of their hair or a bite of the air.
Other clowning gestures for play include placing objects on their heads, playing with their faces and raising their arms.
Brushing with a hand means they want something to stop, while embracing and pulling at the same time means they want another ape to walk with them.
Other gestures include hitting the ground, swatting, grabbing, and dangling upside down.
Although studies of great ape body language have been carried out before, none has focused so closely on the intentional meanings of specific gestures.
The findings don't just reveal how apes communicate - they also shed light on the origins of human speech millions of years ago.
Many of the gestures are human-like, researcher Dr Erica Cartmill told Animal Cognition journal.
"When they wanted to communicate 'come here', one put an arm round another ape," she said.
"One 'stop' gesture was a light tap on the hand - often of an infant - which gets the other to stop whatever they were doing. A fascinating thing is that there's not a great deal of variation between groups of apes. An orangutan in Singapore gestures in pretty much the same way as an orangutan in a zoo in Philadelphia or Wales."
The dictionary was put together by researchers at Scotland's St Andrews University after watching 28 orangutans at Twycross Zoo in Leicestershire, Durrell Wildlife Conservation Trust in Jersey and Apenheul Primate Park in the Netherlands.
Video recordings were made over three months, allowing the researchers to spot 64 gestures. They found 40 that were used often enough to work out their meaning. The action was repeated when a response was not what the ape expected.
Orangutans are the least vocal of the great apes. Their most distinctive noise is the "long call", which lasts up to two minutes and is used by a male on arrival.
Like chimpanzees, orangutans can learn human sign language.
Scientists in Atlanta, Georgia, taught one orangutan named Chantek about 140 signs - which he mostly used to discuss food. - Daily Mail