From the BBC:
Orangutan communication resembles a game of charades, a study suggests.
Researchers from St Andrews University have shown that the animals intentionally modify or repeat their signals to get their messages across… researchers set up a situation where six captive orangutans were presented with a keeper who had treats, such as bananas, and blander food, such as leeks or celery.
The animals gestured to attract the keeper’s attention so the tasty treat would be passed to them.
However, once the orangutans had done this, the keepers did one of three things: they either handed them the treat, handed them the bland food or handed them half the treat. The scientists then recorded their reactions.
“When the keeper gave the orangutan the really nice food, understandably, that was the end of it,” explained Professor Byrne.
“But when the keeper pretended to fail to understand the original gesture and gave the wrong food, the orangutans stopped using the gestures they had used before and started using some different gestures,” he explained.
“And when the keeper half understood and gave the orangutan part of the treat, the orangutans started to repeat the same gestures that they had used, but they would repeat them even more enthusiastically.”
Full story at the BBC