{"fact":"Crows and ravens can learn which tokens are valuable to them, and they're eager to trade those for tasty snacks like mealworms or fried pig grease.","context":"When a subject gave a self-value token to the human experimenter, it received one piece of food reward, but did not receive a reward when transferring a partner-value or no-value token to the human experimenter.","source":"Claudia A. F. Wascher; B'eatrice Feider; Thomas Bugnyar; Val'erie Dufour, Crows and common ravens do not reciprocally exchange tokens with a conspecific to gain food rewards, 10.1111/eth.12970","index":431}