Doctoral student Erica Cartmill found that Orangutans communicate with each other using gestures, and when their point isn't getting across, they'll adapt their gestures to try and better explain themselves:
Orangutans have been taught sign language before, but Cartmill showed that this is how Orangutans normally speak to each other, or at least to humans who have a tasty-looking banana. These Orangutans had not been taught sign language, and two separate case studies were done at different zoos, so this was really Orangutan improv.
My first thought upon reading this was, "this is is a great demonstration of ape intelligence and how they function together in ape culture."
My second thought was, "I would have loved to do this study if I wasn't so worried about getting my arm ripped off if I didn't give them the banana."