In 2006 researchers at the University of Washington put on a rubber caveman mask, caught a handful of campus crows, ringed their legs and let them go. Afterwards, whoever walked across campus in that mask got mobbed: crows diving and scolding overhead. A different, neutral mask got nothing. The surprise came over the following years. The scolding didn’t fade. It spread, to crows that had never been caught and to young birds hatched long after the trapping, who had learned whom to hate by watching their elders do it. So somewhere in Seattle there are crows who have never been wronged by anyone, and know exactly whom to blame.