It turns out long-held resentments exist even in the animal kingdom. Does that mean they hold an evolutionary advantage?The best thing that happened to me during the whole of the pandemic was a story on the internet. An Oregon resident, furloughed, saw on a daytime nature documentary that, if you fed crows, they would bring you small gifts. Curious, they tried it, and were delighted to find themselves in effective possession of a 15-strong crow family – but then things took a dark turn. The crows became an army, fiercely protective of their leader’s property. If neighbours came near, the crows would dive-bomb them. “To be clear,” the person wrote on Reddit, “they’re not aggressive 100% of the time. If just the neighbours are out [on their own porch], they are friendly, normal crows. They only get aggressive when someone gets close to me or my property.”It’s such a lovely phrase, “friendly, normal crows”; it’s just a pity that it’s an oxymoron. Crows are the most prodigious grudge-holders, which a professor of wildlife at Washington University, John Marzluff, discovered by capturing seven of the birds while wearing an ogre mask in 2006. A full 17 years later, crows were still regularly attacking him. Even if you were to query the ethics of his original experiment, you’d have to admit that he paid a high price. How such a thing is possible when the lifespan of a crow is only 12 years is this: not only can they hold a grudge, they can also pass it on to one another. Originally, even birds that witnessed the ogre-trap attacked Marzluff, then over time they transmitted the hostility to their offspring, creating a multigenerational grudge.Zoe Williams is a Guardian colu