Think about the last time you were down on all fours, perhaps looking for a lost contact lens or doing a few push-ups. Your probably rested your weight on your hands, palms down. But Viki, as well as other Chimpanzees, are unable to bend their wrists backwards as you see in this video clip. Thus they cannot walk on their palms and instead use their knuckles. And you thought your push-ups were hard!

One consequence of their inflexible wrist is that chimpanzees are poor at throwing objects. Our flexible wrist allows us to impart an extra “snap” to thrown objects, and also to control the direction of the throw more accurately. But we are not as good as chimpanzees at climbing trees or swinging from branches, so that flexibility may have a cost as well.