{"fact":"Just like humans and some primates, ravens can understand addition and subtraction.","context":"The experimenter placed two small rectangular cardboard pieces on the platform, and lifted an occluder to prevent the bird from watching the baiting procedure. Then the experimenter baited the two cardboard pieces with different amounts of reward (same as in Relative Numbers).","source":"Simone Pika; Miriam Jennifer Sima; Christian R. Blum; Esther Herrmann; Roger Mundry, Ravens parallel great apes in physical and social cognitive skills, 10.1038/s41598-020-77060-8","index":317}