Economist.com | Dog behaviour: "His experiment was simple. He presented his animal subjects with two inverted cups. Then he hid the cups behind a screen, put a small piece of food under one of them, and took the screen away. The animal had to choose which cup to look under. If the experimenter gave no cue, both species got it right 50% of the time, as would be expected. However, if he signalled in some way which was the right cup, by pointing at it, tapping it, or even just gazing at it, a dog would choose correctly every time, while a chimpanzee would still do only slightly better than chance. Chimps simply did not get the idea of social signals of this sort, however many times the experiment was repeated."