From BBC News:
Richard Byrne, an evolutionary psychologist and an author on the paper, said: “When humans communicate, we routinely use our knowledge of what our audience knows and what they don’t know automatically. “We wanted to find out whether the great apes, that have so much flexibility with their communication, do the same thing.” 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.
“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.”
Professor Byrne likened it to a game of charades.