Crows recognise individual human faces and can hold a grudge for years.
Researchers in Seattle wore a mask while trapping and tagging crows. Years later, crows still scolded and mobbed anyone wearing that mask, including birds that had never been trapped themselves.
Why is this true?
Crows learn from each other and pass on warnings about dangerous people. Their brains are large for their body size, with a density of neurons comparable to some primates.
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More about animals
Animals are the easiest place to find facts that sound invented. Three hearts, blue blood, cube-shaped droppings, a punch fast enough to boil water for an instant — every one of these is ordinary biology to the animal doing it. The collection here leans on well-documented behaviour and anatomy rather than folklore, so each entry comes with a short explanation of why the trick actually works and a source you can read next.